Depends . . .
If you live in the snow belt and don't have winter tires or decent all season tires that would be my very first purchase.
Since it's a 2015 I would hope and guess it's broke in by now -- for better or for worse. If in doubt you can always do an oil change to "start" out its new maintenance schedule as maintained and recorded by you.
Otherwise, it depends on what you want to improve . . . or not improve. As a few folks mentioned, take some time to drive it and see what you like or don't like. Some folks rush right out to get a Cobb Accessport to smooth things out a bit in terms of the rev hang . . . other folks want to tighten up the suspension . . . other folks go for a tint job to help with the heat (or cool factor) . . . other folks like to customize the inside or outside a bit to stand out (new shifter knob, mud flaps, body parts, etc.) . . . other folks cannot stand the radio and put their money into a new tuner and/or speakers.
Me . . . I liked most everything . . . and continue to like (or tolerate) most everything. The one thing I could not abide however was the low height of the driver's arm rest and so that was the first thing I replaced.
