Apple had launched its IOS 15.1.1 upgrade for iPhone 12 & iPhone 13 users. The release note had stated that this upgrade would advance the call drop performance of iPhone 13 & iPhone 12. Apple on its supporting page stated that this update is primarily for the iPhone12 & 13 range.

This IOS15.1.1 update carries a figure number 19B81, which is possible as an over the air download on adaptable iPhone and iPad models. This update will be available on the software mechanism in the settings app. the size of the update is 1.44GB.All the users are recommended that to update this software the phone should be exposed to a suitable environment like using a strong Wi-Fi connection. You need to do the backup before you began to installation process.

In Apple's release notes , it is clearly mentioned that 'this IOS 15.1.1 fixes all the issues regarding the call drop back performances on the iPhone12, iPhone13 along with usual bug fixes. Apple didn't provide specific release notes for its iPad OS 15.1.1 

if you are feeling this update is un necessary and have feel dis interested  to update this or if you are not facing any calling issues then just wait for the IOS 15.2 which has been filled with everything which had updated before which includes with the 

1) enhancement to the iPhone 13 pro's macro code 

2)ability for manual scanning of apprehensive air tags

many and more updated version would be released in soon.