My experience on my 6S Plus is completely opposite of yours.
1. CC is silky smooth regardless of how I interact with it.
2. Cellular menu is perfectly smooth especially considering the list of apps is very, very long in my case.
Very pleased with the performance under iOS 9.3 Beta 3.
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Radon, I thought you had moved on to an Android? iOS 9.3 Beta 3 is exceptionally smooth, compares very well with any previous iteration of iOS. Only thing left for me is to see how battery life is on iOS 9.3 Beta 3. Otherwise iOS 9 is ready for production. Heck even my lowly iPad 2 is working nicely! Enough to be able to hang in there until the release of the iPad Air 3.
I wouldn't say beta 3 is ready for production yet. Beta 3 broke tapping on news articles in the Proactive Search screen. (It doesn't launch safari and take you to the article, it just does nothing except highlight.)
Plus other new bugs like the time after unlocking to the Home Screen not showing for 2-10 seconds (or until you launch an app)