Thanks for finding it.If 15.2 is no longer signed by Apple you won’t be able to use it. I’ll look and see and update this post later.
Edit: Unfortunately Apple is no longer signing iPadOS 15.2. Here is the MacRumors article.
It looks like 15.2.1 might still be signed.
Edit 2: Sorry but it looks like Apple stopped signing 15.2.1 as well. You can’t downgrade from 15.3 any longer.
Apple no longer signing iOS 15.2.1, thwarting downgrades from iOS 15.3
Apple has closed the signing window for iOS & iPadOS 15.2.1, which means it's no longer possible to downgrade from iOS or iPadOS 15.3.www.idownloadblog.com
I just wiped the ipad from itunes for the 18472th time and then downgraded to 15.3. It wouldn't let me downgrade to any of the 15.2 files, 15.3 was the only one I got to work.