Apple has not stated such a thing anywhere, but it would seem likely that the 2016 iPads would lose support for upgrades at some point soon.
Somewhere I read that that 15 would be the last version to run on the 9.7" Pro as well. Don't recall where I read that and I don't know if it's official. To the OP, I'm still using a 9.7" Pro and am running the most recent version version of iPadOS, 15.3.1. I've not noticed any performance differences relative to earlier versions. I don't think I'm a very demanding iPad user. I use it a lot but mostly for stuff like reading, web surfing, watching video, etc. It's held up remarkably well. I do think I'll be upgrading in the not too distant future. I'll probably get a pro because of the screen and speakers but a lot of the Pro features are wasted on a person like me.
Has the performance been the same or worse since upgrading to iPadOS 15? I'm not concerned about battery life, just slowness.
The main thing I notice since going to iPadOS 15, is slowness when typing, a bit of a hesitation. Some slowness opening websites. My IPP 9.7 seemed to run best on iPadOS 13. If I could revert back I would.
I left my 9.7 on 13.4 and it's pretty decent. It will probably die there. Same with my mother's 9.7 pro and my sisters's iPad 6 (both on 13.4). I regretted updating my mini 4 to 14, it has become unusable. I might instead update the 2015 pro to 15. I think the additional RAM should make the difference. My 10.5 pro run fine on 15.3.
