That's great - but how do you do it? If I just copy the 375 images onto the video track, I don't know how to do this into a 15 second block - the images just spread out along the track in a seemingly arbitrary way. As you can gather I'm quite new to Vegas Movie Studio!

Depending on if you have a new enough version of Vegas, you may have the "import still image sequence" function. Go to File / Open, browse to the directory containing the images, and click on the first one. At the bottom of the open dialog window there may be a checkbox for "import still image sequence". Check that and click OK. All files with the same name except for sequential digits at the end will be inserted into your project as if they were a video file. You'll be prompted for a frame rate and other parameters.

Note that the files have to be named something like frame0001.png, frame0002.png, frame0003.png ... etc. If there is a break in the numbering then Vegas will stop there and you'd have to import the rest as a separate sequence. However, since most rendering software will name the files in this fashion you are probably already set.

Thank you - that's exactly what I was looking for.

I am noticing that some folders of images allow for the opening as a sequence and some not. Any idea what one folder full of jpgs would cause this while another would not?