Gifts received are not considered income and are not entered on an income tax return.
And $15K is below the form 3520 requirement.
If you, as a US person, receive a gift of more than $100,000 from a foreign person, you are required to submit a Form 3520 to the IRS. Form 3520 is an informational form only. You do not report a gift received on your personal tax return, regardless of the amount received.
IRS Form 3520 - http://www.irs.gov/pub/irs-pdf/f3520.pdf
IRS Form 3520 instructions - http://www.irs.gov/pub/irs-pdf/i3520.pdf
