You do not have to uninstall 1.15 in order to make room for 1.16 in your files/on your computer.
The .exe file should run and the folders should be replaced as required for the update.
What I would suggest is saving any mods you have downloaded/making sure you still have the downloaded .rar/.zip files, as everything alongside the update is reset to a default. This includes mass markings and items.
The items and mass markings .png/.jpg files should still be in your C: > FeralHeart > media > items/textures > markings however, so don't worry about sending all of the items files and markings files back in all over again as you would have had to do before. The only thing you do have to do, is take the items.cfg and markings.cfg from your mass markings and items packs and put it back into C: > FeralHeart.
Other mods you may have downloaded such as maps, interfaces, podiums, etc. may have to be reinstalled.
So make sure you've got those downloads saved somewhere on your computer for reinstallation.
Hope this helps.