Welcome to the Apple Support Communities! I see from your post that the 3D Touch sensitivity on your iPhone 6s Plus feels too sensitive after upgrading to iOS 11. I know it's important to have your phone's settings working in a way that's comfortable for you and works best with the way you use your device. I am happy to help!
It's possible to adjust 3D Touch settings in order to see if choosing a different sensitivity works better for you. Please see the following:
Change 3D Touch sensitivity on your iPhone 6s, iPhone 6s Plus, iPhone 7, or iPhone 7 PlusYou can change the amount of pressure you need to activate 3D Touch.
Go to Settings > General > Accessibility > 3D Touch and slide the sensitivity slider.
On the same screen, you can turn 3D Touch off and on.
Let us know if you have further questions about 3D Touch.
Have a great day!
