Can I use a Mouse with my IPad Pro 2015 version 12.9 screen size

If you have a Lightning to USB adapter you can even use a wired mouse.

I have the same 2015/2016 iPad Pro model as you and I've tried using an older, wired Apple mouse and it works just fine with my iPad Pro on iPadOS.

iPad has limited support for a basic “scroll-wheel + three button” mouse. If you have a more advanced mouse, that requires installation of specific driver software, the mouse will only provide basic functionality.

Use a Bluetooth mouse or trackpad with your iPad - Apple Support