you can make the K10 not rub at the back with 15's and it is really easy, you just need the right bits.
mine used 195/45/15's with spax lowering springs and it was really low. just roll the inner arch lips. you can do this with the Super S kit too, you just have to cut some of the plastic off which attaches to the arch and bond the kit onto the arch, make sure you underseal the inside though.
then you need some decent rear dampers, mine were Monroe Uprated Gas which can be bought from Halfords and many other places and are not hard to get hold of.
dont use aftermarket bump stops which limit the travel of the suspension, use uprated dampers, your k10 will handle much better with better dampers.
My old K10 super s could have 5 people and it would never rub even round hard bends or big bumps.
do it right and you'll have a rubbing free K10!
a few pictures of my old K10