iOS 11.3 (build 15E216) is an official Apple over-the-air update for the iPhone 6s+, released on 2018-03-29T17:12:58Z. The update package is 788.2 MB. This is a delta (partial) update that requires 11.0.2 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 2976102632042653f85379523cb346556dbcb6de.zip.