Here are the release notes from Apple:
iOS 15.6 includes enhancements, bug fixes and security updates.
– TV app adds the option to restart a live sports game already in-progress and pause, rewind, or fast-forward
– Fixes an issue where Settings may continue to display that device storage is full even if it is available
– Fixes an issue that may cause braille devices to slow down or stop responding when navigating text in Mail
– Fixes an issue in Safari where a tab may revert back to a previous page
Some features may not be available for all regions or on all Apple devices. For information on the security content of Apple software updates, please visit this website: https://support.apple.com/kb/HT201222