Lag while using iphone6s

Its an iOS 9 issue, All you can do is wait for the next update or reduce transparency in the settings.

Describe this "lag" you are experiencing in an iPhone 6s. I have a 6s and it is lightning fast. Did you restore this phone from a backup of an older phone? What is actually lagging?

its more of a framedrop than lag in almost any animation. an example would be swiping to go back in the settings app.

Swiping from where to go back to the Settings app, from inside Settings? I've seen no lag in animations or other operations. I have a 6s now, but had a 5s and still have my iPad Mini on iOS 9.0.2 with zero issues as well.

Yes, swiping back from anywhere is choppy for my iPhone 6S. My iPhone 5S is much worse on iOS 9.0.2 as well.

What troubleshooting have you tried? Is this phone a restore from a prior device, as I asked the OP?

I went to the Apple store the third day I got the iPhone 6S and had an Apple Genius restore it. It was still the same and told me to just wait for a software update (9.1).

I suppose you will need to wait, if that is what Apple Genius said. I'm not going to argue, but I don't see it as a problem on my devices, nor any others I know with the software. Good luck.