Hey buba,
I applied there too. In some cases, applying by the "priority deadline" will help you in the ranking system, but mostly it's to ensure that if you DO get accepted, you will be funded. The majority of people who apply do so in early January. The process of admission seems to be a hybrid: on the one hand, they say they have rolling admission, but they also use a competitive ranking system. From what I gleaned, if they REALLY want you, they'll decide to admit you automatically, otherwise you get thrown into the ranking pile, which isn't finalized until after the deadline passes. You should expect to get something in the mail by the first week of March, the latest. Try to relax, I know what it's like, and I'm freaking out too. But also don't get hung up on the "12 to 15" number. Remember, that they will always tend to admit around 40 people (max), assuming that some of the people they admit will accept offers elsewhere. Hang in there, and good luck.