Raise/lower brightness is extremely slow Whenever I try to raise/lower my screen brightness with the F1 and F2 buttons, it takes a couple of seconds before the brightness changes, and I can't stop it from raising/lowering the brightness

Raising/lowering the brightness is also a very slow process

Is there any way to bring this back to normal function/speed?

I have a mid 2012 13" MacBook Pro running macOS Sierra.
I suggest you reset your SMC (System Management Controller).

The process can be tricky, but you will know if you succeeded if the MagSafe Plug light changes color momentarily as you do the reset.

The reset of SMC depends on your Mac model, so follow the instructions here.