I did some more tests today. There is definitely an issue if you have lots of compound and/or multicam clips, then take serial project snapshots -- IOW create snapshot 1 from project 1, then open snapshot 1 and edit that, then create snapshot 2 from snapshot 1, etc. This causes exponential growth in the SQL database. Within a few cycles it will cause rapid onset of a performance problem.
This mainly happens if doing sequential snapshots of projects that contain compound clips and or multicam clips. In general compound clips are more common than multicam clips. If the compound clips are multiply nested, it will happen faster.
Given this understanding, my advice is do not use nested compound clips, and under no conditions take serial snapshots of a project containing those. Rather use the command "duplicate project". If a snapshot is needed, take one of the current project and continue working on that project, not the snapshot.