I'm not negative, I'm shooting it straight from experience.
Since the OP was talking about brake upgrades, they are going to do you no good if your tires suck. Suspension upgrades are a package deal, one part goes hand in hand with the other to get the best out of the investment.
It boils down to; I just don't like seeing people waste money. When at a 1"+ bigger rim you could actually get a tire with some decent tread wear and better compounds. On top of that, these days 15" can actually be more expensive.
If you get them at a steep discount, more power to ya.
Just fair warning.