iOS 11.3 (build 15E216) is an official Apple over-the-air update for the iPhone 6s+, released on 2018-03-29T17:12:55Z. The update package is 1.46 GB. This is a delta (partial) update that requires 10.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 56bb9aa120a1df113c11b8944bbaa108aa326832.zip.