did you actually check to see if 15mm will fit before buying something which is useless in the end? The people that are saying they have 15mm rear ones are also saying that they aren't very low with the car. I am quite low and it seems like you're reasonably low, so I seriously doubnt 15mm will fit.
All i want to say is, check before buying something which isn't that cheap, just to find out you can't fit it.