Hi Simon,
As you already know, Touch ID and Apple Pay (Wallet) on an iPhone 6s Plus does not require the home button to be depressed. This will therefore keep those functions of the iPhone working even if the home button is unable to perform tasks that require it to be mechanically depressed. More than likely your home button will need a replacement.
Before you take your iPhone to have the home button repaired try recalibrating the home button. It is a simple process and see if that works-
Calibrate the home button
- iOS devices support an option to calibrate the home button, which requires interaction with an application like the Calendar, Weather, or YouTube.
- To make use of this option, open one of these apps
- With the app open press the Power button at the top of your device until the "Slide to Power Off" option appears.
- As soon as you see the red slider control, press the home button and keep it held down until the red slider disappears.
If you are in luck then this may make your home button more responsive if other aspects of the button are in working condition.
If the above does not work then you can attempt to clean the area around the home button.
Good Luck.
Axel F.