I've ordered every vehicle I've ever bought going back to the early 70s and have learned a few things about that process.
I know that when I ordered my 2013 F350 diesel that I had it in my hands in less then 8 weeks. I know they can give you a 'scheduled build date' within a couple weeks of ordering - there's a big red flag right there. My dealer sent me an email with that info.
Something is wrong. As stated above, I bet it has to do with the model year changeover. I'm guessing you ordered a 2015 but at this point I'm sure you'll end up with a 2016.
Generally a dealership should be able to tell you what the last date is that you can order a current model year vehicle. You might try and find out what that date was for 2015. I'll bet you ordered during the dead zone; you should have been informed about that.