Yeah, but I have never, ever, used such a poorly-performing version of iOS on any device. I'm not exaggerating, I really think that.
iOS 8.0 kept relatively the same performance as iOS 7.1.2 on my iPod touch 5th gen and my iPhone 5s. I thought it was a solid .x release.
But 9.0 is waaaay different compared to 8.4.1. Lag everywhere, unstable, and a release that's just not ready in my opinion. This is evident on all devices that I have and most of those I've tested at the Apple Store (4s, 6, 6 Plus, iPad Mini 3, 4, iPad Air, iPod touch 6th gen; however, the 5 and Air 2 weren't laggy from what I saw).
Until Apple fixes this, I won't upgrade to it. The new features aren't worth it if the phone performs terribly. 8.4.1 is fantastic in stability and performance.