iOS 15.5 includes enhancements for Apple Podcasts and other features and bug fixes, as well as a baseband upgrade to 1.61.00 to improve iPhone signal performance.
Apple usually stops the verification of older versions of iOS within a few weeks after pushing the official version update. For some users who have updated to the latest iOS system, when they encounter major bugs, the downgrade method can sometimes be very effective.
That’s why Apple waits a while before closing the authentication channel for older versions of iOS. The previously released iOS 15.4.1 fixes the problem that the iOS 15.4 battery drains too quickly.