How to uninstall iOS 15 from ipad

The ability to restore an earlier version of iOS/iPadOS is limited - but is possible in certain circumstances. The procedure is not trivial.

All System Updates are digitally signed by Apple - and can only be installed whilst the digital signatures remain valid. After release of a new iOS/iPadOS version, the immediately preceding version continues to be digitally signed by Apple - however, usually within a few days, Apple will revoke the digital certificate with which the earlier version is signed. After a major update, such as the initial release of iPadOS15, the period that the preceding version is signed my be longer.

Reversion to an earlier version will entail the use of “DFU” mode to reinstall the previous version; all locally stored data will be wiped. If you have an existing iCloud or iTunes backup of your data, your data can be restored after reinstalling the previous version of iOS/iPadOS. You’ll need access to a PC (with iTunes installed) or a Mac (with iTunes or Finder - as appropriate for the installed version of macOS).

Be aware, that you can only restore an iCloud backup that was made for the version that you have reinstalled - or to a later version of the OS. As such, if intending to restore iPadOS14.8, you’ll not be able to install a backup that was made using iPadOS15.

So as to avoid unnecessary description of the process, iMore have a useful article that describes the procedure of restoring an earlier version. The article refers to a different versions of iOS, but the process is the same.

After you have reinstalled iPadOS14.8, you’ll be able to restore your [compatible] backup to your iPad:

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

Hello. You cannot uninstall an iPadOS update. Downgrades from one version of iPadOS to another are not supported.