Go where you want, and feel you'll like, distance is probably a factor that helps crown for you. Plus, it keeps the fees down (transport or almost for camps).
And, if you don't make it, you are not hopeless there are plenty of corps especially div 3 that are always searching for brass players even sometimes up to MAY ...
Plus, talking as a 15-year-old guy that will soon start is third year of drumcorps(will turn 16 in 2006 summer), you will surely love it.
And remember the size of a corps does not necessarely matter. I marched last summer in 35 person corps and absolutely loved it, the family atmosphere was like nowhere else.
Plus, sometimes if you are in a smaller and more local corps tour can be a little shorter and will probably reassure your parents. At least I know it did for mine.
Finally, I must say I probably not the best to give advice on that since where I live (Québec) , there is only one corps in the whole province. So I didn't really chose my corps.
If you speak french or would like to learn there are openings in all section at my corps (Stentors). But, it is probably to far away for you...
Sam