3D Touch is one of the marquee features on the new iPhone 6s. It’s sort of a right click for the iPhone. As you get used to it, you might find that you have to press too hard, or that it activates too easily.
Fortunately, you can adjust this, but you need to know where the setting is hidden. Go to Settings > General > Accessibility, and scroll down a bit. Tap 3D Touch.
There are three settings: Light, Medium, and Firm. Try each by pressing on the photo near the bottom of the screen, and choose the one that works best for you.