I am about 1/2 way thru making a video / slideshow. I am now seeing it run poorly. The choppiness doesn’t bother while I’m working on it. I have about 3 or 4 weeks worth of work into it and about 3 or 4 weeks to go. The finished product will be about 30 minutes long.
Should I stop and fix something now? or can I carry on and figure it out at the end?
If it’s only choppy while previewing it’s nothing to worry about. That’s completely normal unless you have a super-computer.
OK. Yes during preview. I’m not sure what other way to view it. I think you mean I could output it and see the results. (Why didn’t I thing of that) 
If you unset the option “Realtime (frame dropping)” in “Settings”, it won’t be choppy, but it (obviously) won’t run in real-time (e.g. a 5 minute clip may take 8 minutes or more). The EXPORTED end result will be fine in either case.
Not much more for me to add except, remember you can export a segment of your project without having to wait for the whole thing to render if you only wish to see the results of a certain part.