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

Just in time - you can now go ahead and download iOS 15 and iPadOS 15 beta 3 for your compatible iPhone and iPad device.

As usual, the changelog suggests that this update improves performances and fixes bugs. And, it is available as an over the air download for everyone with beta 2 installed onto their device.