I found a web site for the 15th Ark. It list Harris as one of the many commanders of the 15th.
On the other hand "Battles and Leaders of the Civil War" lists Lt. Col. A. K. Patton as commander at Shiloh. Patton is shown as killed at Shiloh so, perhaps, Harris was briefly in command. The 15th was part of Cleburne's Second Brigade of Hardee's third corp.