If you carried forward an overpayment from your 2015 tax return to your 2016 tax return, that money will now factor into your 2016 bottom line. If your bottom line shows an overpayment for 2016 (which will include that amount carried forward), then you can simply have it all refunded to you on the 2016 return.
When you indicate that a 2015 overpayment should be carried forward, then once IRS processes the return, that money will no longer be part of your 2015 "account." The IRS shifts it to 2016 and it gets applied to your 2016 return. Then you can take the new 2016 overpayment as a refund, or you can carry some/all forward to 2017, and so on.
When you file the 2016 return -- assuming you have another overpayment -- TurboTax will ask you whether you want to carry any of it forward to 2017, and you can say no, which means you'll get it all back as a refund.
