As it turns out, not so well. According to a recently published video on YouTube from Adrian Isen, he pits two iPhone 4S handsets together. One of them runs on the latest iOS 8.3 while the other runs on the early iOS 9 beta. Now we should note that given that this is only the first beta, there are bound to be issues as it is still relatively early into development, so the end result might be completely different.
That being said, so far the initial impressions that the video has left us is that the iPhone 4S running on iOS 9 is noticeably sluggish compared to iOS 8.3. We suppose this is to be expected since the platform was probably designed for Apple’s next-gen iPhone in mind, although on Apple’s website they do list the iPhone 4S as being one of the supported devices.
Like we said the phone running the iOS 9 is running the first version of the beta that was released to developers. We can only assume it has not been fully optimized so there is a chance that the final release this fall could be better, but for now it looks like iPhone 4S users should not expect too much from the update.