Apple has today released iOS 9.0.1. This is a small update that brings performance improvements and bug fixes. In this update we see a fix where devices froze on the setup screen, alarms would not play, pausing and distortion in Safari and Photos, and where APN users would loose their cellular data.
This update can be obtained from Settings > General > Software update > iOS 9.0.1. On an iPhone 6 running iOS 9 it comes in at only 35 MB.