A MBA won't be able to max out WoW. So he needs to get a 15" MBP with an ATI 6750m or ATI 6770m. ( or the ATI 7XXX when the 2012 MBP is released. )
The OP asked about 15" Air, and considering none of know the specs, or even if there's going to be one I don't think any of us could recommend that it won't work. My post referred to the base 15" MBP