As soon as
DCL release the 2015 cruise schedule, you will be able to book a cruise for 2015 using
DVC points. As far as DVC is concerned you already have the points, and for cruises you can book ahead as much as 24 months out, if the cruise line schedules are released.
We once booked an Alaska cruise for Aug of 2011 in Aug of 2009 with 2010, 2011, 2012 points, so if can definitely be done. Just call DVC after the cruise line releases the cruise you want for 2015, you will have to borrow if you need points from 2016 for the cruise, which, of course cannot be reversed, if you decide to cancel.