My Ford ordered over ten years ago and Ram ordered last year arrived as expected. My guess is that your dealer missed the cutoff to order 2015 models and yours was delayed while tooling was reconfigured for the 2016's. Although I have read posts where people follow their build daily, I just wanted a date when the build was expected to start and when the truck would be available for pick up from the dealer (I wasn't going to sit around and watch the water come to boil).
I keep my vehicles longer than the average, so I don't mind waiting to get exactly what I want rather than settle for what is in current inventory. I use more than one vehicle for my daily commute, do not trade in vehicles (sell on my own) and do not make a purchase contingent on a sale, so buying and selling is a relaxed process for me with few time constraints.