I've heard it is still pretty bad from several people.
I strongly suggest waiting out 9.0 until 9.0.1 is released, which is what I'll be doing, or try out 9.0 first on a 5s at the Apple Store to see if it's fast enough for you before upgrading.
I have the 5s and I've already had to restore twice from the iOS 9 betas because of terrible overheating and lag issues. I'll stick with the super-smooth 8.4.1 until 9.0.1.