 Head coach Bill O’Brien retained Mercilus and Clowney as the starting outside linebackers to begin the regular season in 2015.During Week 8, Mercilus collected a season-high seven combined tackles and recorded 3.5 sacks as the Texans defeated the Tennessee Titans by a score of 20-6.In the regular-season finale, he recorded five combined tackles and tied his season-high of 3.5 sacks during a 30–6 victory over the Jacksonville Jaguars.