How to Prepare for the iOS 9.3.5 Update
It's difficult to predict how the iOS 9.3.5 update will impact your iPhone 6s' performance. That's why we recommend doing a little prep work before you make the move.
If you decide to install iOS 9.3.5 on your device, please take a look at our list of things to do before installing the update. These are the steps that we take before every single iOS update and we've escaped the iOS 9.3.5 release (so far) with a solid piece of software.
At the very least, know that you should make a backup of your files/data before you download and install it. It's better to be safe than sorry, even with a tiny update like iOS 9.3.5.