Many students who send music supplements to Yale are conservatory level performers. This is the level of quality your recording will be compared with–so it is up to you and your teacher to decide if it is. I think the number of years that you have studied will not even be a consideration, if you list those things on your application that you mentioned in your first post: that you are principal in your youth orchestra, have won a number of competitions, assistant principal in an adult orchestra, etc. That alone shows admissions that you are an accomplished musician. (And, it is my understanding that admissions will not even forward the recording over to the music department unless you are already considered to be a strong candidate based on your application). I would hesitate sending a music supplement unless it is of the very highest level of performance ability.