I figured that was Tamiya White .
It's really good stuff but it's high solvent --- so it drys fast but lots of shrinkage .
Best for shallow / fine repairs but you can build it up .
Try Squadron Products " Green Putty " for a putty with more solids than solvent .
15 psi is pretty nominal -- never hurts to experiment though . Seems to be OK ?
... you generally want to spray at the lowest pressure you can .. but it will vary from paint to paint
El MoMo ;D