When someone takes a plea deal, the reduction is included in the sentence for "taking responsibility". Unless he has some information that will help the authorities solve another crime, he is likely to do 85% of the sentence. You might ask to see the Judgement and Commitment document from the judge's office, if there is a parole provision (state only) then there is some possibility for reduced time if the parole board elects to approve him for supervised release.
https://www.inmateaid.com/ask-the-inmate/my-husband-got-sentenced-to-22-yrs-max-for-2nd-degree-murder-he-took-a-plea-is-there-any-way-we-can-get-his-sentenced-reduced-he-has-served-half-of-the-time#answer
Accepted Answer Date Created: May 06,2015