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 iPhone8,2
iOS Version 11.2.1
Release Date 2017-12-13
Update Date 2017-12-10
Sha1sum
62309429f83eb96041d5f3ddbae3a7580d13ee91
Sha256sum
afbc7353b41a844b77a9f25e87f0ccb2cf7ba11a9d33524b8059d43ce8cc64cd
md5sum
b7b7ca626eea70cc44a95ad303e8bc1d
Size 2.61 GB
FileName
iPhone_5.5_11.2.1_15C153_Restore.ipsw
Status

Download IPSW (2.61GB) 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