I really enjoy using the 3D Touch features on my iPhone 6s Plus, but if you’re not a power user or if you have a difficult time with the subtle dexterity 3D Touch requires, you may find yourself frustrated when you accidentally press the screen too hard. It’s especially apparent when typing or rearranging icons: press too hard on the keyboard and the keyboard blanks, or tap and hold icons to rearrange—but don’t hold too hard or nothing happens at all.
To modify the sensitivity or to turn off 3D Touch entirely visit the Settings app > General > Accessibility > 3D Touch.