Subaru did a very good job with the 2015 WRX's suspension. Ride quality is excellent on the highway. Firm enough to feel sporty, but not rattle your kidneys stiff. They have beafier anti-sway/roll bars, stiffer springs, and better valving in the dampers, all in an effort to make the most of the improved chassis. And, while this is an all new chassis, most of the suspension components are from other platform's parts bins. We quickly found out that coilovers from the 08-14 STI would pretty much just bolt on to the 2015 WRX, with only one very minor modification required. We plan to try out a few different coilovers to see which we prefer, but we got started with the Cusco Zero-A coilovers.
The Cusco 692 60N CP Zero-As are intended for the 08-14 STI and come outfitted with adjustable front and fixed rear pillowballs and have 7kg/6kg (392lb/336lb) springs. These aren't a huge amount stiffer than the stock rates. They aren't crazy, race car stiff, so they will make a decent street-car-that-goes-to-the-track suspension. The front adjustable pillowballs mean you can easily adjust the front camber and should be able to get -2.5-3.0deg depending on ride height.
The Cusco dampers are a claimed 40-way adjustable, though that is single adjustable and anyone that knows anything about single adjustable dampers will tell you that you will never notice a difference from one click to the next on something that adjustable. You may feel a difference from one extreme to the other, and maybe from one end to the middle, but only if you are very in tune with your car.
Install on this car is very straight forward and the same as on the 08-14 cars so we aren't going to go into the step by step. There is a minor modification needed in regards to how the ABS sensor attaches to the front struts. On the 08-14 cars there was an ABS sensor wire guide that screwed into the strut, and all 08-14 coilovers have a place for that guide to screw in to. On the 15 WRX Subaru changed from a screw to a plastic clip.
Most coilover manufacturers will undoubtedly come out with new part numbers that have the clip in bracket for 2015+ cars, but you can make the 08-14 components work by removing the clip and using a zip tie to hold the sensor wire in place. Race car engineering at its finest.
One last word of warning: The rear suspension components are covered in sealant. It is a black, sticky, tar. Wear disposable rubber gloves when working on the car. Have a rag to wipe off your tools.
Once you are all set on your ride height make sure you go get an alignment. Your camber and toe will be wonky. While -2.0 to -3.0 degrees of camber won't hurt good performance tires, any significant amount of toe will. Bad toe settings also make for a darty, twitchy, and an unpredictable car.
As it sits now we are 1.4" lower than stock all around. -2.5d camber on every corner. With the big wheels and tires we got a very small amount of rub on the rear when we hit a tall joint between the highway and a bridge (it was a lot of compression at 80mph with three people in the car). Just enough to transfer paint from the fender lip to the edge of the tires. We are taking the JSCRedWRX to LIP Collision on Thursday to get the rear fenders rolled.