iOS 11.3 (build 15E5211a) is an official Apple over-the-air update for the iPhone 6s, released on 2018-03-12T17:05:47Z. The update package is 228.77 MB. This is a delta (partial) update that requires 11.3 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 80072f0342252898edf9b2e5bd84bd3c5ac6f4c4.zip.