Wow this thing is very complex. As far as I can see Tracks 1-16 do nothing. But maybe I missed something.
The rest is 2 sets of Parent Motion namely tracks 17 to 32 and tracks 33 to 42 .. The controlling tracks are 17 and 33. They both are keyframed to slide the image, titles etc in left to right and then hold. To understand what's going on, you need to know about Parent Motion,.
I believe Eagle Six has already figured this out and what he has done should work. Brilliant.
The speed of the slide from left to right does not change unless you change the Parent Motion track keyframes that control the slide. But you can lengthen out the time after the slide is done by doing CTRL+drag to extend all the tracks in each group once the image has stopped moving. The important thing is to divide this into two groups, Tracks 17 - 32 and 33 to 42 and to understand the Parent Motion. Track 43 is a white background that needs to be there for the entire timeline.
As I said, this is very complex and I still might be missing something.
Indeed it is, but I got a lot of missing files and plugins after the download of your veg, but now I don't know what you want to achieve exactly.
To extend the available Vegas options and pictures you have to do and delete first a lot from that veg, like
1. deleting the trackgroups that hold nothing and the empy tracks
2. cut the parts off at the incisions in the tracks that sign that those have have been lenghtened already because of their probably already stored lenght in the original Vegas version
3. and Ctrl-drag those remainings after have grouped them.
This is my remaining video after I did some of those things