Hello,
I downgraded from 0.15.10 to 0.15.9, and I got this message when starting a new game : "Map version 0.15.10-3 cannot be loaded because it's higher than the game version"
This is a Steam install, and I downgraded via the Steam interface, selecting the .15.9 in the game properties.
[15.10] Map version issue
Re: [15.10] Map version issue
That's because it's trying to load files created in 0.15.10 in 0.15.9 (player data, blueprint storage, save files, and so on). Older versions of the game can't load newer versions of the game.
If you want to get ahold of me I'm almost always on Discord.