iOS 11.4 (build 15F5061d) is an official Apple over-the-air update for the iPhone 6s, released on 2018-05-01T17:06:05Z. The update package is 214.75 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: cbc7653dd1787ad49a085a3a22b0299132415f35.zip.