I've built an app in Xcode 6.2 and it was running fine but when I moved it Xcode 6.3 on another system I'm getting a lot of Swift compiler errors.
Most of them are like "AnyObject is not convertible to NSArray", "AnyObject is not convertible to NSNumber"
Sorry I could not upload any image.
I would strongly advise reading the release notes in order to get a rough idea of what has/hasn't been changed.
There are some major syntactic modifications and a few depreciations, which you will have to manually fix in your code.