Yes, 15% of working capacity is the ordinary entitlement of the away team supporters for FA Cup ties. That can be reduced though, if safety considerations warrant it. Man Utd fans didn't take too kindly, just a few years ago, when Arsenal denied them such an allocation, so I'd expect an allocation of some 9-10,000 for this game. The draw couldn't be very much worse for us really though, as United I'm sure will be looking to the FA Cup as their best chance for silverware this season.