iOS 11.4 (build 15F5071a) is an official Apple over-the-air update for the iPhone 6, released on 2018-05-07T17:11:47Z. The update package is 225.65 MB. This is a delta (partial) update that requires 11.4 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 207aff336045381484748daf25581fdf12d32322.zip.