Saw files are expensive and retoothing saws will eat them up quickly.
In this case, since the teeth are nice and even already, I’d recommend living with the current 12 TPI spacing. Joint the teeth if necessary. File the teeth straight across to eliminate fleam. Set the teeth if they need it. (They probably won’t.) If you need the saw to cut more agressively you can go back and refile the teeth with less rake.
Then if you aren’t satisfied you can do something more radical: either retoothing or simply buying a saw with more TPI.