You're skiing Griffons right?
What are they currently set to? If I was you I'd start off at 6 and go from there.
Here's the bit where we get all serious-faced about knee injury and put the fear of god in you. I'm not a doctor, but I've gone through the whole ruined knee business and it SUCKS.
Being 15, you're probably approaching skeletal maturity but it's possible that your growth plates (the bits in your bones that do the actual lengthening) aren't finished. If you tear an ACL, the conventional way (if you're using a patellar graft) of replacing it involves drilling into your tibia to insert a bone plug that's attached to the graft. If your growth plates aren't hardened yet, there's a good chance this will cause them to freak the hell out and stop growing properly. The worst case scenario with that is that your tibia stops lengthening while the other one continues, and you end up with different length legs. While this is real handy for traversing (in one direction only), it will seriously screw your skiing life up when they want to repeatedly break your leg and put it in traction until it's the same length as the other one.
When you're like 18, 20, that kind of age, your bones are significantly harder and the potential consequences of an ACL injury are considerably lessened. Also you'll bulk up and have more muscle to protect your ligaments in a crash.
Unless you're skiing in a manner that a ski coming off at a bad time would cause more injury than it not releasing in a crash, take the hits and keep your DINs sensible.
Sparknotes: I think 10 DIN is way too much for you. My friend who is an ex racer, instructor and general madman skis on 10, and he weighs quite a bit more than you.