'slow enough' is correct and can be used in written English.
You can use it when referring to the speed or rate of something. For example: "I walked slowly enough to make sure I didn't miss any details."
This gives us a slow enough rotational speed for counting.
And slow enough to relax and enjoy the meal.
The book starts slow enough as it is!
The game was slow enough as it was.
Also, the cationic exchange kinetics are slow enough to allow for direct interrogation by XRD.
In a closed universe, rays of light would eventually return, if the expansion was slow enough.
Your own workplace may be slow enough (it's summer) that you have the extra time.
But New York's progress, along with that of Florida, has been slow enough to raise concerns.
In fact, when reheating is slow enough, the volume actually shrinks in the transition range.
Her class is slow enough that you can settle into the right alignment.
Syracuse is more athletic, but if the pace is slow enough, Wisconsin could make things difficult.
