Installation Issues & Other Day One Problems
You can count on iOS 9 release date problems.
The iOS 9 update is in the spotlight right now and the focus will only intensify once it's announced on stage during the iPhone 6s launch event. And we expect that to cause some installation problems in and around the update's release time.
We almost always see sever problems and installation problems impact iPhone and iPad users during peak hours. There will be a huge rush to download iOS 9 and all of its features and you can expect to see some initial hiccups (lengthy download times, errors) as Apple and its servers try and handle the load
We expect download and installation times to vary but you should certainly set aside an hour or more to complete the download and install process.
We also expect there to be a number of day one iOS 9 problems. Problems always emerge after iOS updates, even ones that spend months in beta like iOS 9. iOS 9 is focused on performance but you can still count on some bugs and isolated issues slipping through the cracks.