Magic Trackpad 2 became less responsive
There's probably a few things you could try (e.g. making sure the trackpad has a decent charge, resetting the NVRAM and/or SMC etc).

However, the first thing I'd try is to reset both the macOS Bluetooth Device List and Bluetooth Controller. 

IMPORTANT: This will reset all connected Bluetooth devices, including any bluetooth keyboard or mouse, so all Bluetooth devices will need to be reconnected.

Before commencing, you will need to have the Bluetooth icon showing in the menu bar. If it is not there, open System Preferences > Bluetooth and enable the option Show Bluetooth in Menu Bar.

Resetting the macOS Bluetooth Device List and Bluetooth Controller

Follow these steps:


Hold down both the Shift and Option keys and at the same time click on the Bluetooth icon in the menu bar. Once the menu is showing, release the keys.     
From the Bluetooth menu, choose Debug > Remove All Devices
Hold down both the Shift and Option keys again and at the same time click on the Bluetooth icon in the menu bar. 
From the Bluetooth menu,  choose Debug > Reset the Bluetooth Module
Restart your Mac
Setup your Magic Trackpad 2 again
Setup any other bluetooth devices


Let us know whether this helps.

As for how long it will last, the Magic TrackPad 2 was only launched in October 2015, so it's too early to say. However, if the original Magic Trackpad is anything to go by, you should get years of service from it.