iOS 9.2 is a milestone upgrade and Apple's larger point updates always come with a collection of bug fixes for lingering problems.
There are iOS 9.1 problems and there will be problems with any update that Apple puts out between now and the iOS 9.2 release. Software is never perfect.
Expect the iOS 9.2 release to tackle some iOS 9.2 problems. Developers have already spotted several fixes on board including performance enhancements for the iPhone 4s and the company's 5.5-inch iPhone 6s Plus flagship.
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