MacBook Pro fan won't shut off system super slow

Thanks. If you dig down into the links within that document, you will find the following passage.

"If the fans in your Mac run fast even when it isn't experiencing heavy usage and is properly ventilated, you might need to reset the System Management Controller (SMC) on your Mac."

We can be more specific if you are as well. Please tell us your macBook Pro's SUB-MODEL, from "About this Mac..."

Macbook Pros have been continuously made since 2006 in easily hundreds of variants. Older 13-inch MacBook Pros showing slow behavior usually have hard drive issues; in newer MBPs with fast solid state drives, slowness has to be something else. There are also differences in the sensors that controll fan speed.

So posting more details will help you get suggestions specific to your sub-model.

Identify the apps or processes burdening that Mac: See how apps affect Mac performance, battery runtime, temperature, and fan activity - Apple Support