For your late additions, use the specified amount regardless of AA. They are for flavor and aroma and add a minimal amount of bittering. If you reduce your 15, 5, and dry hop additions, you will NOT have a Sierra Nevada clone, just a mildly hoppy beer.
*edit: As a matter of fact, I have no hard numbers, but the lower AA on your bittering addition is so slight that the higher AA on your 15 and 5 additions just might make up the few IBUs your short from the bittering addition. I can run it through beersmith for you, but I need your OG.