How to not lose Alpha 15 saves upon Alpha 16 release

Just a quick PSA:

Alpha 16 release is upcoming (though no date is announced and we don't know when it'll be final). If you are in the middle of a game, please use the Steam betas feature to set your game to the “alpha15” branch. This will prevent it from automatically-updating to A16 upon release and breaking your save games.

You will be able to, of course, set your branch back to 'default' whenever you wish.

(To change your beta branch, right-click RimWorld in the Steam library, open Properties, go to the Betas tab, select the branch you want.)