Unfortunatly SOA is really only willing to warranty "stock" cars. In my personal experience the secondary warranty's purchased through credit unions or banks are more lenient about aftermarket installed equipment because they allow 3rd party shops to perform "warranty maintenance"
Before you run out and start modding your brand new car I always reccomend that drivers who are new to the platform drive for 3-4k miles. You will need to spend a thousand miles breaking the car in anyway and the extra few thousand miles will help you decide what is truely needed to make it run the way you want. If you want a little extra power and extra sound I would wait until Cobb releases a 2015 compatible accessport and a SF intake. They arent out yet but Cobb is pretty quick to release products for new model years. I just did the accessport and intake on my 13 and the sound is excellent.
13 WRX Hatch - Torqued Performance Stage 1+
Slow is Smooth > Smooth is Fast