If they had, how could there possibly be $15 of arb with CampBX? I don't use Mtgox so I don't actually know, but I can't imagine this situation coming about any other way.
CampBX has seriously low volume. It's hardly ever worth trading there.
I bought a couple thousand USD of bitcoins from them a month or two ago. Express mailed them a money order. Cheap and easy, without the Coinbase delays. I was impressed.