Thanks. Spotted it. We'll check it out.
Did you test the linked VP version? Have you tried the None (CPU only) option?
Looked pretty good using the slightly older 16.09 (64-bit) release. When downloading, ignore any virus warnings.
Allow the project to fully cache. The ribbon under the preview will turn gray...

That done, still see some freezing towards the end, unless PV is repeatedly stopped/started.
If changes are made, such as moving an overlay, some re-caching will occur, but still may be playable in PV during that period.
GPU registered up to 100% during this process, at certain times. On export it was in the 60-75% range.
Check your PM for the output, which was made at 854x480 res.
Two things you might try, to lessen demand on resources...
Break up the project into smaller segments, export each, then assemble those exports for the final.
Or you might create proxies of the two large files and use them in editing. See the Proxy Editing FAQ above. That is a technique that's commonly used to speed and smooth editing while lessening PC resource demands.