iOS 9.2.1 (build 13D15) is an official Apple over-the-air update for the iPhone 4s, released on 2016-01-19T17:59:41Z. The update package is 816.2 MB. This is a delta (partial) update that requires 8.4 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: c6cd62b7be90ffd16306ba39b7f593e1cd7d3db6.zip.