Response times after each stage of selection can be highly variable. I think they process the results in batches so if you're lucky you'll be one of the last in your batch and it'll get marked pretty quickly, but if you are unlucky you could be the first in your batch and have to wait the full 15 days. It took just over a week to hear back from both stages 1 & 2 for me, but judging by many other peoples' experiences this was pretty fast (a fair few people have been waiting 10-15 working days).
I wouldn't worry about it too much, I know its annoying and you are probably checking your emails every 15mins all day, but they'll get back to you when they can and the length of wait you have to put up with has absolutely no bearing on whether or not you've passed. The whole thing is a pretty long term process so you'll have to get used to waiting for a bit.