Wheel size for track?

[MrHanky]

Hi,
 
My preparation continues to get my EGI ready for track day use this year and I just wanted to ask what size wheel would be best for track use?  I ask this as my car came with a set of 17" Advans and a set of 15" Mazda wheels (did the EGI come with stock 15\'s or are they from another model?).  Anyway im just wondering which ones I should use?  
 
Any help would be much appreciated.
 
Thanks
 
Mark