As long as the $15,000 in funds are sent / wired electronically (and not in cash, where there is a special reporting requirement for all transactions in excess of $10,000), then you shouldn't have any particular problems, as far as this concerns United States compliance and tax reporting requirements.
There is such a thing as a US gift tax reporting requirement (i.e., filing a Form 709 gift tax return, but not necessarily paying any actual gift taxes), where the amount of the gift is greater than $14,000. However, this proposed $15,000 would not be considered a gift, since you're not keeping it, and are simply acting as a "middleman" or flow-through conduit. Neither is it considered taxable income (or a deductible expense) to you.
So, from a compliance perspective, I can see no adverse tax implications to you, if you don't keep any part of the money, and simply use your US bank account as a pass-through mechanism and favor for a foreign national friend, to pay off a US debt. Of course, your friend could probably also wire / pay the debt himself or herself, directly, through a foreign bank account in another country as well, even if a currency translation or an international transaction fee would result.
Either alternative should not incur any negative consequences for you, however.
