Rear sprocket change advice?

I have a CFMoto 450MT

It's gearing is a bit on the shorter side, when buying it I for the dealer to install a 15T front sprocket, so the top speed is at 160kph (100mph)

I'd like to reduce rpms a bit further, without having to shorten the chain or anything like that.

Would going from a 47T rear to a 45T be a good way to achieve that? How noticeable would the torque decrease be? Is it even good for the sprocket/chain if the current set has 9500km of range? It's not noticeably stretched or anything like that, but the teeth do have some wear on them, and I'm aware you shouldn't really replace just one part instead of all three (chain and 2 sprockets) at once.

What do you guys think?

Thanks