I don't think the pressure would be the problem if the conversion is correct? or at least not the only problem. (dont get me wrong the compressor is no way ideal but should work)
I spray paint alot lower than that sometimes below 10 psi with no problems (different airbrush tho) I think that you are likely to have a blockage in the nozzle, I personally would try spraying some airbrush cleaner through it and give it a thorough cleaning if that doesn't work then I would try a different compressor if possible (doesn't have to be one designed for airbrushing any good hobby/work compressor would do the trick).
Good luck and let us know how you get on.
