Compressor gauges typically read a different pressure when air is flowing and when it is not. Normally you would adjust the pressure when air is flowing since that is what is important to you when you are using the brush.
I'm not familiar with your compressor, but 12-14 psi may be all it is capable of doing. I wouldn't think so, but it could be. That's the pressure range I like to paint at, but I would think you'd be able to get a bit more out of it.
What do the specs for your compressor list as max pressure? And does it show a "Working Pressure" or anything that is lower than the max?