Reduce 85% mandate in illinois for first time offenders

Recently a loved one was sentenced to 37 months in prison for aggrevated DUI. He must serve 85% of that sentence. While I realize that a crime was commited, my loved one is far from being a violent offender. This is his first offense . Before he was sentenced, he was working every day as a heavy machinery mechanic. He paid his taxes and was a law abiding citizen. He is an honest man who mad a terrible mistake and he has to live with that every day. I have watched him and he is tortured by this. Now, he is serving his sentence in a prison in Illinois. Instead of paying taxes, he is costing tax payers money. I don't understand why he cannot qualify for any good behavior and get his sentence reduced so he can continue to contribute to society and be a good father and grandfather to his family who has already lost one parent due to this tragic accident.