Apple brings App Thinning with iOS 9, by theory, the thinning process is done on apple's server, I understand it as apple compiles my App from bitcode to machine code.
So if I submit an App built with iOS 9 SDK, will Apple also slice my package for older version iOS systems like iOS 7 and iOS 8?
According to App thinning Docs:
Note: For iOS apps, sliced apps are supported on the latest iTunes and on devices running iOS 9.0 and later; otherwise, the App Store delivers universal apps to customers.
So devices with iOS 7 and iOS 8 installed will receive the universal version.