It depends. Your 2017 refund may be delayed or offset by your 2015 deficiency.
You received the letter because you didn't report some of your income on your 2015 tax return. However, the letter does not necessarily mean you owe the money to the IRS. Regardless, this issue needs immediate attention.
If you agree with the letter, then respond and pay as soon as possible. If you do not agree with the letter, then follow these steps:
Read the IRS letter you received carefully. Compare the letter to your 2015 tax return. What is the letter saying is missing? If you can't make sense of the letter, you can either call the IRS for clarification (1-800-829-1040) or visit your local IRS office in person. Visiting in person may be the better option as the IRS agent can provide a transcript of the document you didn't include with your return.
Next, use the missing document to complete an amended return (1040X) in TurboTax. If the end result matches the IRS letter, before penalty and interest are applied, then you need to pay the IRS the balance due from the letter. If your amended return shows something different, then file your amended return to the IRS, along with your letter and the balance due (if there is one).
You may even get a refund. It can happen. It just depends on the circumstances of what information didn't get reported on your 2015 tax return.
Follow the steps listed in the TurboTax FAQ below on how to complete an amended return. Click 2015.