Download iOS 11.2.1 (15C153) for iPhone 6s

You will have to note that you can only restore signed IPSW firmware files using iTunes or 3utools.

❌ This IPSW firmware is not being Signed by Apple

Firmware Identifier iPhone8,1
iOS Version 11.2.1
Release Date 2017-12-13
Update Date 2017-12-10
Sha1sum
202b14e1e0f2cdbffc9a08c3aff9a75a4d9c1eee
Sha256sum
a50333cdc2199845c9e4ccc080bc68c0f30a5b22cc87ff30765d2594781e7cb7
md5sum
d2ad5a1613a62b5170615d97d3de29b2
Size 2.47 GB
FileName
iPhone_4.7_11.2.1_15C153_Restore.ipsw
Status

Download IPSW (2.47GB) Check device info
Release Notes

It should be noted that these are the official release notes for the from Apple

iOS 11.2.1 fixes bugs including an issue that could disable remote access to shared users of the Home app.

For information on the security content of Apple software updates, please visit this website:

https://support.apple.com/kb/HT201222