I have done it a couple times and I believe it is 15mm socket. There is not much room. I cut out a hole under the drain plug so I dont have to remove the shield next time. That is the only pain in the ass for the whole process.
Several members on F150forum.com report completely removing the cloth/carpet shield whatever it is and never looking back.
I put mine back in place after first oil change. But I had the young guys at the car wash do it while I supervised.