Glad I just went back to iPadOS 15.6 to get the 8-9 hour of screen-on time back. On 15.6.1 I got 3-4 hours of SOT (11” iPad Pro 3rd generation). Strange enough on my 13 Pro Max SOT didn’t have that drop, but still was not on par with 15.6 so I downgraded my iPhone too. For me 15.6 is one of the best iOS 15 versions.