im not him, but i know a thing or two about e-tunes. its when you data log your car (on my legacy you would hit the defrost button) do a pull to redline, hit the button again to stop the log and thats your data log. The tuner tells you what parameters he wants logged and you choose them before the pull. After you finish the log you email the tuner your data log, he looks at it makes adjustments that he thinks are necessary and emails you back a revised version. you flash the new map on and do it all over. its honestly a pain in the butt but i did it before and car ran pretty good (07 legacy gt spec B).
so pretty much your driving the car and data logging, emailing the datalogs to the tuner and wait for a new map. i think e-tuning can be pretty good as long as the tuner is good and you know what you want the car to feel like. one e-tuner that i really liked when i talked to him was Ron @http://www.phatbottituning.com or his partner known as STI-mikey. but i only talked to Ron. have a few friends who have tuned with him and love it.
He requires you to have access tuner and a access port. don't do Romraider, once you try access tuner after romraider you'll never go back.
if some of this stuff doesn't imply for your 15 sti, my apologies they are so new i havnt gotten a chance to learn much about them yet.
on Rons website go to etuning, and he tells you a little about what it is and what he wants logged. I'm not saying you need Ron to tune your car. he didn't tune mine but was going to until i decided i wanted to do it with a friend to learn all i could and am happy i went that route.
there are many many tuners out there, but most of them i won't allow to touch my cars unless i have hard core evidence they know what they are doing. but in all seriousness if i were you, a pro tune would be the best. you wouldn't have to be speeding around on public roads, it'll be a one day thing (should be lol) and you'll love it. But pro tuners tune to there driving style thats another disadvantage...