So beginners should start with internationals and gradually move up to Level 15?
While there are degrees, there is indeed some merit to this. L.10 is much easier than vets. We take a new ref, fresh out of the box, and ask ourselves what is the best environment for him to develop his skills. Then we tell him to go police 30 players who have been conning far better refs than him for the last 25 years. I find that bizarre - while Vets treat the outcome of a game as a pretty inconsequential side-effect of their warm-up act for the evening's drinking, they are more than happy to play their well-honed tricks on a green ref.
I think there's a lot to be said for exposing a ref to the vets at L.10 as a management challenge, once he's got the basics under his belt.