Besides having the driller watch him throw the ball, as has been suggested,
What surface is on that Wrath SF?
Stock polish?
It got pretty good length and was for medium-light to medium oil as are most Vibes. If he can't get it through the heads, I doubt if he will get any Vibes through the heads either.
First, I'd make sure one ball is highly polished, like sanded to 4000 and then firmly polished with something like Storm's Xtra Shine, Brunswick's High Gloss, Powerhouse Factory Finish, Valentino's Snake Oil, etc.
I also wonder if that ball speed, 15.5, is at the release point,not the backend. Around here on AMF/Qubica machines (measured at the pin deck), 15.5 is pretty firm speed.
He may need either a lighter ball, or a really mild ball, like Tropical Breeze, Strike King, Ascent Pearl or Scream.