Apple has provided developer beta testers with third builds of iOS 15.6, iPadOS 15.6, tvOS 15.6, and watchOS 8.7 to test out.
The newest builds can be downloaded via the Apple Developer Center for those enrolled in the test program, or via an over-the-air update on devices running the beta software. Public betas typically arrive within a few days of the developer versions, via the Apple Beta Software Program website.
For the moment, it seems the releases are largely bug fix and performance improvement editions. The main focus will be on the other set of the same betas for the milestone operating system versions: iOS 16, iPadOS 16, tvOS 16, and watchOS 9.
Apple also released the third developer beta for HomePod software version 15.6 to AppleSeed testers.
The third build number for iOS 15.6 and iPadOS 15.6 is 19G5046d, replacing 19G5037d. The third tvOS 15.6 build has been updated to 19M5046c from 19M5037c. Lastly, the third watchOS 8.7 beta build is 19U5046b, taking over from 19U5037d.
AppleInsider, and Apple itself, strongly recommend users don't install the betas on to "mission-critical" or primary devices, as there is the remote possibility of data loss or other issues. Instead, testers should install betas onto secondary or non-essential devices, and to make sure there are sufficient backups of important data before updating.