According to my information 15 quarts of oil.
I have not changed mine yet (only 1,900 miles) but I will take it in after my upcoming trip. Still won't have anywhere near 15K miles, but from a time standpoint I don't want to stretch it out longer. Should have around 5K when I take it in August.
Plan to use my local Freightliner dealer (Young Truck Sales, Canton, OH), they have been excellent to deal with in prior visits regarding my parking brake recall, the shift cable noise, and the purchase of my fog lights and all associated wiring and switches. And they cut me a big price break to enable the fog lights in the multiplexed Freightliner electrical system.