If this is already mentioned then feel free to ignore/delete.
Its not something thats too bothersome, I think it was also in VP14.
If I do say 30-50 snapshots or more, Vegas can eventually freeze up and become unresponsive, entails using task manager to close it. I guess in some way taking snapshots must use a lot of memory, maybe not released back? I have 16GB, of course its just a guess that its memory related.
I can usually see a slow down and close and restart to prevent freeze up.
Select the shots you want, and save them as an image sequence.
Since this is a built in script, no need to save individual snapshots from the preview buss.
Not sure I follow, do you mean somehow multiselect different points on the timeline? then run a script to save the selections as an image sequence.
What I sometimes use the framegrabs for is to put a series of them at the end of the project.
If I don't do that then there there saved in my Frame grabs folder and can be if needed say printed, emailed etc.