You just proved yourself you are an idiot.
What you have is an evidence that you have sent some BTCs to MtGox.
MtGox filed for bankruptcy, meaning all funds are frozen, and creditors can't touch whatever MtGox has until some court order. Go ahead read mtgox.com and get yourself informed. All you can do, at this moment, is to cross your finger, and pray perhaps, for a court order in your favor. And that Mark will remain faithful and accountable, that he will do his best to regain funds to return what's yours and other creditors. But can we trust his word? And when can we get our money back? Many creditors don't have enough faith for that. So, there even may be some deal that Mark will agree to pay only 50% (or whatever portion) of debts in timely manner. I will say it would be wise to be a part of that bargain. It's better than nothing, right?
Otherwise, you are on your own. And if you decide to take a different action, your legal fee would be 100 times larger than your initial loss. It sucks. The truth is too harsh, and difficult to swallow. You just spent 15BTCs for a lesson of life time. I will say it's well spent, and not too expensive.
If you haven't learned anything by being Goxed, you are really an idiot.