I have been making builds using Xcode 5.x so far. My app size (Estimated app store size) was around 55MB. Just after updating to Xcode 6.0.1. The same app is now showing 145MB. I read in few places that it is showing download app size. But this is just a speculation.
here is a link for people facing same issue http://forum.unity3d.com/threads/estimated-app-size-increased-considerably-on-newest-unity.269245/
This is a Unity game. Is this only related to Unity's exported projects or this is a new behaviour of Xcode's "Estimated app store size"?
Finally i got my game approved from Apple and the size is 56MB (same as the build made with Xcode 5.X). So i am now sure that Xcode 6 shows downloaded size of the app or as it appears from my experience.
So don't worry :) your app is going to be what it should be.
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