Note that any amount of your excess from 2015 that you apply as a contribution for 2016 would not be an excess for 2016. If you made a new eligible contribution for 2016 which blocks you from being able to apply more of your excess from 2015 as a contribution for 2016, you can request a return of some or all of your new 2016 contribution to make room to apply more of your 2015 excess as a contribution for 2016.
