I got a chuckle from

Mouse : Logitech Promethus Spectrum 502

PC Gaming will be a far better place if all you have to do to get major boost in performance is to swap you mouse.

I know you wrote that with a smile but the wireless vs wired mouse folks are very set in their ways as to which is better.

Won't comment on wired vs wireless issue, but having a gaming mouse with configurable keys makes things a lot easier.

i5 2400 CPU: Still a very good CPU for gaming, I have one myself.

16GB Ram: It's more or less the standard amount these days on a medium-high end gaming rig.

GPU: Your issue is right here, as others have already said, it's weak. If you're on the hunt for a budget graphics card, the GT 1030 or a used 750 Ti are both adequate for the game (also good for many other AAA games).

Or, if you have some financial wiggle room, there's the GTX 1050 Ti - on it you can play The Witcher 3 @ 1080p / 60fps with almost everything on High & No Hairworks (I've got one myself and can personally confirm it's got quite the bang for the buck).