Following the release of iOS 15.2.1 earlier this month, Apple has ceased signing iOS 15.2, the previously available version of iOS that was made public on December 13. Because iOS 15.2 is no longer signed, you cannot downgrade to it if you have already updated to iOS 15.2.1.
In order to encourage customers to keep their operating systems up to date, Apple typically stops signing older versions of software updates after new releases are released.
iOS 15.2 features a number of major enhancements to Apple’s mobile software, including App Privacy Report, Emergency SOS, Legacy Contacts, a new Apple Music Voice Plan, and more.
Meanwhile, iOS 15.2.1 addresses an issue that prevents Messages sent via an iCloud Link from loading, as well as a bug that prevents third-party CarPlay apps from responding to input.