Prefer the rotation rate that is easier to control
The instructor says roughly one to one-and-a-half inches of face travel corresponds to a one-degree face-rotation change, and within that variance the golfer still controls the face. They directly compare two rotation rates: they do not call the 30-degree rate bad, only that the likelihood of control is higher at 15. They add that going back to something more conventional is a different proposition than staying at a rate where the face is controllable like that.
Channel: Club Champion
Watch official source at 8:30Why this context matters
The measured rates and control windows are specific to this comparison.