WP may not pass iOS's market share in the US market by 2015, but it is growing by leaps and bounds in many of the other major markets (e.g., Europe, Russia). A large part of this success is thanks to the lower-end Nokia Lumia models like the 521, which are competitive with lower-end Android phones on price while being generally higher in quality.
I have a running bet with a friend that it will be. I made the bet several years ago before its actually starting to do in other markets already.
When I made the bet my friend (who works in the cell phone division for an large multinational) was adamant that Android would take over. In the past year the company has decided to removed all Android devices due to support cost/issues and moved to iOS. (I don't know the specifics as to what the android problems where, so don't bother asking, but he said management was very unhappy with them).
I don't see iOS being more useful to a business in the long than windows phone. I'd say in two years time when they review purchasing again that iOS isn't the favored choice, and my bet finally come to fruition.
I hope nobody is seriously putting money on the windows phone passing ios by 2015. The odds have got to be at least 500 to 1 it doesn't happen.