If you need some sort of catchy 'saying' to help you remember the enforcement of DPI, try this:
Thinking from the previous spot:
"It's 2:15, Les."
That is a morphed version of "S(pot), (B-)2, (or) 15 (yards), (whichever is) Les(s).
Replace "S" with a sound-alike contraction (It's); "2" means the B-2; "15" means a full 15-yard penalty; and "Les" means whichever is the lesser penalty.
An exception you'll have to remember is DPI fouls when the ball is snapped on/inside the B-2 are 1/2 the distance (even if the foul is in the field of play).
Another special case is DPI fouls on Tries from the B-3 (or less): 1/2 the distance to the goal (even if the foul is in the field of play).
Not trademarked. Use it if you wish. Just get it right.