If we get 15k to the game then we need to win, everytime we've had big crouds before the team has failed to lift for them. It's going to be hard but at least its Adelaide. It could very well be a 0-0 draw with two teams that cannot score playing each other.
But as said it shouldn't be about the crouds, if you look at our stats we tend to do 8-9 k throughout our history and pretty consistantly. There has been the first year when we got more than 11k, and a couple of years when averaged 6k but most of the time its 8-9k which is pretty good for a city of our size even when you compare it to countries that Football is dominant in. I heard somewhere that the Phoenix are the fourth most supported team in the country, presumably after the Warriors and the top couple of super rugby franchises.
If they didn't want crouds of 8-9k then they shouldn't have setup in cities the size of Wellington, in fact they shouldn't have an A-League at all because only the Victory, the Roar, Adelaide and the two Sydney teams manage it consistently. All this talk about fishing where the fishes are doesn't work, just look at Heart/City without derbies their crouds are similar to ours.