Apple has released tvOS 15.5 and HomePod software 15.5. The former is, as best I can tell, a maintenance release with bug fixes and performance tweaks.
You can install tvOS 15.6 on your Apple TV set-top box by going to Settings > System > Software Update.
HomePod Software 15.5 is, per Apple, an update with “general performance and stability improvements.” You can update your HomePod or HomePod mini through the Home app on an iOS device.
