The game doesn't require installation, just download and play. If you download the new version and just open the 1.5 game, you can still play your 1.4 save in it.
Yes. It will be in a separate folder. I have a folder called Raft, and I put 1.3, 1.4, and 1.5 inside of it. They don't install, so nothing replaces anything. You just extract the folder with the game in it.
