Is there a possibility to mount a 2014/2015 Croozer Cargo trailer hitch onto a 2012/2013 model?
Maybe.  It depends on differences beyond the hitch system for the trailer.  Best bet is to find the model you want to upgrade to and take measurements and compare.  

Typically you will find that the trailer tongue is made of plain tubing (be it square or round).  I doubt that this will change much between model lines and years.  What will change is probably the various bends in it to give the tire some clearance.  The important part is that it is the same size tube on the inside (or really close).  The hitch parts are then inserted into the tube and secured with a nut and bolt.  If the inner diameter is good and the securing bolt is in the right place, make the swap.  

I have done such swaps on both of my trailers.  My kid trailer is a Pacific Voyager 2 and the other is a generic cargo trailer (happens to be a Asom Wonderer, but other sell it as well).  Both trailers had a spring that came out of the tongue into the quick release assembly which then attached to the component that is mounted on the bike.  It ends up that both trailers have tubing that is the right size for the Burley systems so it was a quick swap.  All I did was undo the bolt, slide out the spring, then add the flex connector and bolt.  Here is a picture of the setup from my cargo trailer: