Correct me if I'm wrong but IOC did indeed slip to 2019 if they followed the OTE schedule like initially planned.
It's only because the MARINES opted to declare IOC themselves, a prerogative every service has, that we are maybe going to see an IOC as early as 2015.
I don't know if the USAF has done the same with their 2016 plan but I clearly remember GEN Bogdan commenting on the 2015 MARINES date.
Looking at all that needs to be done and tested ,2019 seems very likely which is why the NAVY sticks with it , it seems.