Looking at the pictures of the tires on your car again they are definitely sticking out past the fender, looks like you have the correct rim though. I checked american muscle's website and the model number for the 15x8 is 92-580150DP with a back spacing of 5.3 and an offset of +19mm
2014 Mustang GT 6R80, Procharger Stage 2 D1SC, BBK 85mm TB, Boss IM, Sai Li fuel system. Circle D 3C, 1-7/8" Kooks Long Tubes w/Offroad X Pipe, Lethal Over-Axle Pipes, Corsa Quad Axle-Back, Eibach Pro System Plus, BMR K member, Shaftmasters DS, Forgestar CF-5 Wheels and Nitto NT05 tires. Lund Tuned
Lots of suspension goodies and some other stuff I can't remember.