You can download iOS 15.7.2 (19H218) from here and use it on supported iDevices. This is currently compatible with the iPhone 6s and is being signed. That said, before downloading this IPSW firmware file, make sure to check the status below.
As you can only restore signed IPSW versions, only download this for updating if you see it indicated "Signed: Yes"
iOS 15.7.2 (19H218) for iPhone 6s
✓ This firmware is signed. This means that you can restore to it in iTunes.
Release Date 13th December 2022
Upload Date 2nd December 2022
Filename iPhone_4.7_15.7.2_19H218_Restore.ipsw
Filesize 5.28 GB
SHA256sum 79395e1f4bce5a4c7283d917d39cee71d8d3338dea1234f480371852e44edaed
MD5sum c0bd22c4b8a57068a81e7723111be4d3
SHA1sum c6ad05343f0e5580904d0af9c3ae392fa0068dee
Identifier iPhone8,1
iOS 15.7.2 Release Notes
This update provides important security fixes and is recommended for all users.
For information on the security content of Apple software updates, please visit this website: https://support.apple.com/kb/HT201222