It's entirely normal the "slow" rotation of the *Parking* object ( and the Parking system and Marshaller ) is "slow", because there you need the utmost precision to align with the ground markings and, it has been like this in GSX for a long time.
Note that, we don't increase the speed, since we cannot obviously move anything on the screen screen any faster than the actual frame rate so, what we change from object to object, is the amount of degrees that are changed at each rotation step so, your perceived speed is also depending on your frame rate.
However, there's is a reason why a FAST rotate command exists so, it's not as if you are stuck into slow motion. The normal way of rotate an object is to first use the fast rotation ( F7/F8 by default, or the MOUSE WHEEL in P3D 4/5 ) to get close to your desired heading, then finely adjust it using the slow rotation.