No, it is not okay just to put it on your 2016 taxes. You would be required to file an amendment for your 2015 return and include the 1099-R on your 2015 return.
Code P indicates that the taxpayer contributed more than allowed to a 401k, IRA, etc. (through payroll withholding), and must include the excess contributions as income for the year in which the contributions were made. If the excess contributions have not already been claimed in that year, the return would need to be amended to include the excess distribution as income.
