My .02 is to break up that 15 min. addition in half and add the other half at 10 minutes. I would also add that extra .5 oz at 5 min as well. If that makes your IBUs too high, I would lower your 60 min addition to 1oz and maybe add the difference at the Dryhop. I have an IPA that has medaled twice using Simcoe at 15, 10, & 5 minutes and it has a very smooth hop flavor.
Simcoe is a terrific flavor and aroma hop and I think your current recipe will turn out great. Good Luck!