https://wccftech.com/download-ios-15-3-and-ipados-15-3-rc-now-available/

Developer and testers can now go ahead and download iOS 15.3 and iPadOS 15.3 RC builds for iPhone and iPad right now.

Apple has been seeding iOS 15.3 and iPadOS 15.3 updates to developers for a while now and the company has finally published the release candidate builds to developers and both public beta testers. If you're enrolled in either one of the programs from Apple then you can go ahead and download the near-final build over the air.