OP,
Go for it. I have a 2013 now and send in the oil for sampling every 5k. It's been great. Nothing earth shattering. I've had several 7.3's, several 6.0L's, two 6.4L's, and this one 6.7L. ALL were great motors. I've logged a couple million miles across all of them, so they got used. I know most of the owners who bought the trucks, and they all have over 100k on each and are happy with them. Check out your used one before you buy it. I get so fed up with the bashers of all brands it makes me sick. Blah, blah, blah. People rarely come to boards to praise, but moreover to crab. I frequent the truck boards, and the 6.7L has been the best motor since the 7.3L. The 2015's are getting poor fuel economy, but running strong. Jump in... The waters fine.