iOS 11.2.1 (build 15C153) is an official Apple over-the-air update for the iPhone 6s, released on 2017-12-13T18:13:28Z. The update package is 1.13 GB. This is a delta (partial) update that requires 10.0.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 90e59a7ae92b121c67e245dd012d32c3c9435faa.zip.