Reducing Storyline file size?

Disclaimer: my team is stuck using a 2-year-old version of Storyline (3.65.28121.0) because that's how government IT works. :/

We have a large project that was outsourced to a vendor a couple of years ago due to lack of staffing. We are now revising the course internally, but are publishing only the interactions for an eBook course. So we'll take a large lesson file (100MB, for example) and remove all the slides except for the 2 or 3 slides that are a knowledge check for republishing. So the project file is now only 3 slides, with zero audio and zero graphics. Yet the file size is still 100MB. I've tried a Save As a couple of times with some success, where the resulting file is a more rational 700kb. But that approach is hit or miss. Often I just end up with a new file that's also 100MB. Clearly the project file is hanging on to a bunch of hidden cruft it doesn't need.

I've also tried copying those 3 slides and pasting into a new Storyline file, but of course that results in formatting/design problems we don't want to have to fix manually.

Is there a way to get these stripped-down files down to the appropriate stripped-down size?

Thanks.