Be it the 3115 or amending, you're talking about amending 10 years of tax returns. If amending any tax return before 2017 results in a refund to you, and you will not be getting that additional refund. But on the downside, if it results in you owing more taxes to the IRS, then you do have to pay that along with interest and any penalties, fines that may be assessed. While a CPA may be able to negate or reduce penalties and fines, they can't negate or reduce any interest. While the IRS can forgive fines and penalties, by law they can't forgive interest if applicable.
Let a CPA handle this, for your own piece of mind.
