You have three years from the due date of the tax return to file for a refund. So you must file a 2015 return no later than April 15, 2019, to claim the refund. You can find prior year tax forms from the IRS at https://www.irs.gov/forms-pubs/prior-year.
Debt on which a person is not personally liable. In case of nonpayment, the creditor must foreclose on property securing the debt. At-risk rules generally bar losses where there is nonrecourse financing, but an exception applies to certain nonrecourse financing for real estate.