Use the Faster Touch ID
During setup Apple only prompts you to register one fingerprint with the iPhone 6s, but you can register five of them. The new Touch ID sensor is faster and it is certainly worth using. You'll be amazed how fast Touch ID works on the iPhone 6s compared to the iPhone 6. It's worth trying out on your own. If you still don't like it, you may want to set up a 4-digit passcode.