If the income was received in tax year 2015 (calendar year 2015) then you need to report it on your taxes this year. Employers are required to submit to the IRS any 1099-misc they issued so the IRS will be looking for you to be reporting that income (they do a match on their end). If you don't report it you will get what is called a CP2000 notice from the IRS telling you you failed to report income and they will likely charge penalties and fees.
If you've already filed your taxes, and the status is "accepted", then you can easily amend your return with TurboTax. Sign back into your account and where your filed return shows accepted, there is an option to amend.
