2015+ Performance Pack is manual trans only. I opted out of the PP option because I daily drive and take on long trips. I wanted a spare tire. It's also an option. You put mismatched rear tires on the Torsen diff, you will destroy it.
Autos quicker, but manual is more fun. If you get a manual, replace the shifter with a Barton or MGW. Replace fluid with BG fluid. Clutch is a POS. Prepare to replace it with something better. I'm eventually installing a McLeod RST dual plate. Car rides much better with Steeda Progressive springs. Test drive carefully, some of the S550's have a reputation to have bad vibration issues from 45-70 MPH. Reportedly an easy fix by shimming the crossmember down 1/8-1/4". Ford refused to admit an issue and dealerships have been trying to fix things by swapping parts, but no one will admit it's a drive line angle issue.
Exhaust is way too quiet. Plan on replacing that too, if you want it to sound like a performance car and not a Prius.
If you plan on supercharging or the Shelby intake upgrade, prepare to swap out the oil pump gears at the same time. Stock cannot handle high RPM's and they will come apart at 7000 RPM's and wipe out your crankshaft instantly.
Paint is very thin and chips and scratches extremely easy.
If you work on your own car, get a set of Steeda jacking rails. With the IRS rear, it makes putting the car in the air much easier.
I've had my '15 since Nov 5, '14. It's been a blast to drive. Sure, it has a few negatives, but the fun factor outshines the flaws.