1500 psi will still give you a good number of shots, no problem.
The problem this guy has/had was that, like mentioned by Matski, the output pressure on the AIR had not been set yet, so it was on loooooooooooow. So even if he had a full 4500 psi fill, he still would have had the clicking sound.
It wasn't his marker, so he didn't know the workings......