So, here's a quick follow up and review of my eventual workflow (mainly so I can remember it myself!) using the help and advice from you all...

I updated the NVIDIA drivers, and also updated my Windows 10.
I set RAM preview to 400 (I have 32MB RAM so I thought his would be ok)
I set my preview to Auto (still not quite sure about all the different settings in the preview window, many seem to be counter-intuitive!)
I used Irfanview to change the jpegs to PNGs and reduced their size to 2880px on the long side
I then reduced the size of the PNGs again by 25% in Irfanview (I know I could have done the last 2 steps in one operation in Irfanview, but, living and learning!)
I edited the project using the low quality PNGs (all less than 1 MB) on the timeline. There was no lag or problem with timing.

I then changed the folder name so Vegas used the higher quality PNGs
On initial playback there was some minor lag and stutter but after it had played through the timeline once (it's only 1:30 long) this disappeared and it ran perfectly
Just as a test I replaced the first 12 images (there are over 100 in the final project) with the original jpegs.
The lag and stutter was back making it impossible to work, so it seems certain that Vegas has a problem with jpegs (which, in my opinion, is unacceptable in a program with such a history)

Thanks to all who offered help and advice, it's appreciated.

 

Something is still not right then but I don't have a clue what it would be unless it is something in that version of Vegas. I am on version 12 and have done several slide shows with jpegs (with at least 100 slides) and only the occasional stutter. Sorry I can't be of more help.

I thought to gave enough evidence with the video of a project with more than 1000 jpegs with way more than HD resolution and effects, that it should be able to use jpg pictures or this program without a problem and with full preview.

Yes, sorry, of course you did. I mistakenly thought you had converted the jpegs to PNGs but that was another poster in this thread. There is still something wrong as david-tu said, and it is extremely annoying after spending a considerable amount on a custom-built laptop that I just expected to do the job.
I'm going back to the UK in December so maybe I can take it back and get someone to take a look. It is out of warranty but I don't mind paying as long as I get the performance i need.
Thanks all again.
 

You could zip up a sample project and media and share it (e.g. on Dropbox, Google Drive, OneDrive, mega.nz, wetransfer.com or mediafire.com) for users here to test on their systems.

You could zip up a sample project and media and share it (e.g. on Dropbox, Google Drive, OneDrive, mega.nz, wetransfer.com or mediafire.com) for users here to test on their systems.

Great idea, thanks. I'll do it immediately.

So, here is the Dropbox link to my project:
https://www.dropbox.com/s/kxluderbucltcow/Neo%20Blue%20Car%20Seat%20test%20Nov%202017.rar?dl=0

It contains the following:
* 2 short samples (12 seconds long) of the actual project using the first 12 images
* one version has jpegs on the timeline, the other has PNGs
* I have also included 2 videos of what happens to each project when I run it
The PNGs version runs smoothly, the jpegs stutters and makes it impossible to edit to music

Please don't worry about the Radiohead copyrighted music! I will replace this when I have time to write another piece in this style.

Thanks for any further help

Bundling the actual pictures in the zip would enable us to see if we get the same issue.

The projects have interlaced settings, unlike the screenshot in your previous comment. Is there a reason for that?

I exported the projects as Vegas Project archives and selected "include media", so they should be there.
No reason for the interlaced settings.
I didn't set this, but I have done so many tests, exporting and importing onto the timeline, I may have done it accidentally (don't know how!)

I exported the projects as Vegas Project archives and selected "include media", so they should be there.
No reason for the interlaced settings.
I didn't set this, but I have done so many tests, exporting and importing onto the timeline, I may have done it accidentally (don't know how!)

Sorry, I could have just checked the .rar filesize to see that the images are not there. I have no idea what it means to select "include media" if they are then omitted!
I'll do it now and update the link.

Here is the link to the jpegs.
I am uploading the PNGs now (also the "No Surprises" MP3)
https://www.dropbox.com/s/sov91gyn7c57cpx/Neo%20Blue%20Car%20seat%20edits%20year%201%20jpeg%20images.rar?dl=0

Untill you provide us with your stills I made a quick test with both projectfiles with content replaced with my own stills on my laptop from signature..
test 1 with replaced jpg's and properties

video test 1

test 2 with replaced png's and properties

video test 2

Only the text in test 2 lags a little

 

The text is not correct anyway, I was editing it when Nick suggested uploading the projects and I forgot to delete it when I exported it.
It will be interesting to see what happens when you use my images as yours have no lag at all.
Thanks

At least we are getting somewhere and hopefully closing in on the actual issue!
My images are 3 times the size of your also, is that significant?
I also don't know what that difference means.
Here is the link to the PNGs and audio track, which may be irrelevant now.
https://www.dropbox.com/s/i9piqlfdug11xmu/Neo%20Blue%20Car%20Seat%20edit%20year%201%20PNG%20images.rar?dl=0

Thanks again

It depends on the size. I have reported these problems with stereo images in the German forum and also MAGIX a while ago. Unfortunately, proxies for images are (still?) not supported and must be managed manually. Here I hope for MAGIX.

I meant the filesize of the jpegs was 3 times larger, but as I said, I don't even know if that is significant.
Thanks so much for trying this out, I will give this a go tomorrow.
I was hoping that Vegas Pro 15 would solve the problem, but as you had the same issues I'm glad I didn't buy it.

I found this tutorial about the Dynamic RAM preview setting. If this is correct, changing this setting should make no difference to the preview window when running normally on the timeline.
https://sony-vegas.wonderhowto.com/how-to/avoid-choppiness-when-playing-back-video-sony-vegas-401566/
Cheers

I found this tutorial about the Dynamic RAM preview setting. If this is correct, changing this setting should make no difference to the preview window when running normally on the timeline.
https://sony-vegas.wonderhowto.com/how-to/avoid-choppiness-when-playing-back-video-sony-vegas-401566/

The Dynamic RAM Preview max setting is probably the most mysterious setting in the entire history of Vegas. It's more complex than simply setting aside a chunk of RAM to use for Dynamic RAM Preview, as that video says. Its effect need testing on a per-system basis.

Thanks to you both. You would just think that after Vegas being established for so many years, someone could clarify this without ambiguity. There should be a straightforward, clear explanation of precisely what happens when this setting is changed.
I've been so close to giving up on Vegas so many times as I just want things to work as they should. It would be stupid to give up something you love if there's nothing around to replace it though!

The total amount of pixels of your jpegs are not 3 but 2 times the amount I use.

I tried to make a slideshow the way I usually do with a few of your jpegs.
In that case the lagging is worse. So I tried some what to do about it.
Best method for me and my laptop is to use Tools/Render to new track.

I did it and made a screengrap of using this.
In the video you see first playing with muted "new track" and afterwards playing with the "new track". That new track you better have only to use for previewing your edits.
If you like the way I made that kind of slideshow you can download a test.veg with some of your jpegs, where you can find what and how to do it.

Link:

The test video showing the use of "new track" :

I couldn't try this as I only have Pro 13 and it wouldn't open the file from your newer version. I get the concept though and I think I can try it out without your file. Thanks again.