You will NOT have to start new saves to get 1.5 content. You will if you want ALL of the 1.5 content. You can't shuffle the mine or CC without starting a new game, and if you're too far along, you're past the point where you can get certain new cutscenes. All of the late-game 1.5 content, however, and there is a lot of it, will be easily available to you. (Just remember that you will have to play at least 1 day after the update before you start getting in-game mail about the 1.5 content.)