If you can't stand iOS 11.4.1's performance on your iPhone 6s or 6s Plus, you're on your own.
Apple's stopped signing on iOS 11.4 which means you can no longer downgrade your iPhone 6s or iPhone 6s Plus in an effort to improve performance. Once you move to iOS 11.4.1 you're stuck until Apple rolls out a new version of iOS.
Unfortunately, Apple's stopped signing on the iOS 11.3.1 update and older versions of iOS as well. This won't change in the future.
If you're struggling on iOS 11.4.1 you'll need to find a fix on your own. If you're interested in downgrading a future version of iOS, our guide will help you do just that.