yep mine are 15s and ive got the big brake conversion....
only thing is if there the standard phase 2 16v wheels you will need to space them out by 8mm, otherwise the caliper will strike the alloy, it only cost me about £20 to get the spacers and longer bolts in the end.
as far as im aware these are the ony wheels that have this problem cos of there design, when i had my 8spokes on there it was fine without.
looks alot better aswell and its easy enough to fit if you are a little handy with a spanner.
or maybe a uprated caliper, ie 4pots/6pots... if your on the track your going to seethe benefit there, again i think Ktec do all that.