I\'ve been going backwards in Git history to find the cause of a humongous file size change, but the only real reason I can find is the switch from Xcode 6 to Xcode 7 GM.
Most likely caused by BitCode, I have seen the same growth however once deployed from the App Store the app size hasn't actually grown.
You can disable BitCode in your app and the other targets as well and you should see a shrinkage.