The latest update to iOS comes after numerous user reports of call drops on iPhone 12 series and iPhone 13 series devices. Now, Apple has begun seeding iOS 15.1.1 with the sole purpose of tackling these issues.
The only info mentioned in the release notes for the new update is that it improves call drop performance on iPhone 12 and iPhone 13 models. The update weighs in at 385MB. Apple is also supposed to release iOS 15.2 this month which should bring a plethora of changes and bug fixes including App Privacy Reports, updated Emergency SOS, notification summary improvements and a new child safety feature set.