Not a tech, but have purchased over 10 sets of tires that I had Road Forced when purchased. 15 is my go to number, if they can't get it below 15 I have them order another tire, never had a problem with this at Discount Tire.
The best I've seen is 6, worst is 45 (on a out of round rim).
On my 2014 Accord one of them is 22 and I haven't had any problems with it, smooth as glass.
One thing to keep in mind on the numbers is what is the application. Truck, sedan, supercar? I've seen truck tires where 45 is good, sedans 25 is tops for me, on my Carrera 15 and under is my goal.