iOS Xcode development on MacBook Air 2015
MacBook airs are computers generally aimed at people travelling a lot but have lots of intense work to do with production etc. If you have a different MacBook that has more power I would say it's a good choice. Overall, the xCode 6 would run on it. 

However, for the price the new MacBook comes and the specs it has, I would suggest gathering a little bit more money and investing it in the MacBook Pro 13". It comes with a 2.7GHz i5 processor, 8GB or RAM and a better graphics card.