That's a good point. However, in the demonstration of Karl Rohrbaugh on You Tube, his R9 performs at 25 yds with good results; 15 yds should not be a problem.
I have not experienced any problems at these yardages. I agree, 15 ft. would be a better starting point. Karl starts out at 7 yds, then goes to 25 yds.
He makes the same point; most encounters come at close range. The 25 yds just proves what the gun can do.