The 15x9 +10 should stick out 1 inch more out of the fender compared to the 15x8 XXR you had.
When you lower a car, since the spring are shorter in length, you'll make the shock itself lose traveling it had. By the same time, your changing the suspension geometry. By affecting that geometry, the wheels will sunken into the fender more. The more you lower the more they will sunken and at some point, you'll get negative camber.
So for example, a 15x9+10 will poke more on oem height than the same wheel with a 1'' drop.
Why don't you go with a 16'' or even a 17'' wheel? It will be easier to get a tire to stretch on theses size.
Look at this link, there a huge collection of pictures of stretched tires on many size.http://tyrestretch.com/
Plus, a bigger size in wheels, with stretched tires, you'll have less of the ''boat'' feeling when taking curves. Steering respond is better too.