I was in a similar position my senior year of high school :) I was missing too much class for performances and felt stressed. Unfortunately, I felt like I had to choose between school/career or ballet. As you know, there is little rational for doing ballet only a few hours a week, since you won't be able perform or be very good.
However, ballroom is much more flexible, and it is possible to dance it socially (without a huge committment). Of course, the sky is the limit, and there are amazing dancers who I am sure train rigorously, but it is not that "all or nothing" feeling you get from ballet.
Why don't you take a few classes and see if you enjoy them? I recommend trying different dance styles and different studios. I am at an Arthur Murray studio now (occasionally taking classes and workshops at other dance centers) and love it! I took classes at a few independent studios before (which was great - much less serious though) and a class at college (which was not my cup of tea).
It is pretty exciting too, that you can continue enjoying ballroom throughout your life, where ballet is more challenging to integrate into your life in your 20s and beyond.
Have fun + good luck!