OK, here's what I've done and learned so far, but first let me clarify something before sharing the project. In the procedure you described for making the backup folder, I did note that you said NOT to include the VJP file. Well the backup folder DOES include the VJP project file. If I remove the project from the backup folder,there will be nothing but clips and audio. So if I don't see how anyone else can test it or advise without that. But I'll wait for your answer before proceeding.
That said, here is a summary of everything tried and learned so far. When I mention "problem", unless indicated otherwise, I'm referring to the lagging caused by preview building.
1) Selecting my video card, default, or CPU only had no noticeable effect on the problem.
2) After cloning my system to an SSD (Crucial BX500, 1TB), I was happy to see a marked improvement in boot time, speed of launching programs, and disk read/writes (I did a few windows-10 built in tests). However, the "preview building", though improved, was neither eliminated significantly. Not surprised because watching the CPU performance showed near full utilization of all 8 cores (FYI, this machine has two 4-core intel chips , each ES5430, 2.66Ghz, so total 8 cores).
3) Next I re-booted into one of the HD from which I cloned my SSD. I then installed the latest 64 bit version from your link (v16.55 ), confirmed it should instl "over" the old one, then loaded the project. This enabled me to make a direct comparison of performance, without the added SSD Noting the high CPU usage during initial project loading I always wait a minute or so before proceeding further. Running the project I was once again disappointed to see significant hesitations for Preview building. I can't say there was NO improvement, but not significant enough for me to consider the fee for upgrading, unless I discover a lot of new features I want. I will say that when allowed to idle after a project loads, the new version does seem to do better. So maybe my suggestion to let preview building continue in the background has been added. However, any changes to clips or effects will slow things down again. One flaw I've noticed (a flaw in my opinion) is that the newest version does not distribute the CPU usage among all my cores very evenly, compared to my original (v.13.8). With the latest version, the 4th core in CPU #1 is being significantly favored. (I would show you a screen shot of the CPU performance graphs in my Task manager, but I don't see a way of adding a photo here).
4) I am waiting for a response from NCH to see which of my downloaded versions from around 6 months after my purchase would work with my existing licence / registration. As soon as I get confirmation, I will install the one they suggest on the SSD clone, and let you know of any improvements there. Currently the "latest" version I installed at your suggestion says "Licenced Software" in the top Windows banner, but that may just be for a new "trial" period.
All for now.