The more interesting change appears in the security notes. There’s a single security fix for a nasty HomeKit vulnerability, in which a maliciously crafted HomeKit accessory name (containing some 500,000 characters) could cause iOS and iPadOS devices that loaded it to be disrupted, even after rebooting—the only solution was to reset and restore the device. Security researcher Trevor Spinolas reported the bug to Apple way back in August 2021. Unusual though the vulnerability may be, it’s distressing that it took Apple as long as it did to acknowledge and fix the bug—Apple only benefits by treating security researchers well.
If you use HomeKit or have been affected by the Messages or CarPlay bugs, you should update right away. Otherwise, we recommend waiting a few days to see if any issues crop up.
You can install the iOS 15.2.1 update (804.8 MB on an iPhone 11 Pro) and the iPadOS 15.2.1 update (676.6 MB on a 2020 iPad) in Settings > General > Software Update.