crap. Campus PPD just told me, "No sir, that unit you thought was 15 tons is actually only a 7.5 ton unit".
Well.. Let's see, my calculated heat load was around 6 tons, and then the left over space cooling is substantial, so yeah that'd explain why it isn't keeping up...
I need to have a long talk with the engineer who told me that unit was 15 tons. Unfortunately, tracking him down as of late has been about as easy as finding unicorns.