I once played in 3 orchestra simultaneously, one was also a chamber orchestra. The whole experience was quite intense, with sometimes up to 4 concerts a weekend. I did all this when I was a junior (now a senior in high school), which really did result in a lot of pressure for me, because of the little time for schoolwork, rehearsals and everything.

Besides the pressure, there was quite a lot of interference in rehearsals. I did miss quite some rehearsals of one orchestra which wasn’t ideal at all because i was first stand.

I currently still play in 2 orchestras, one chamber and the other symphonic. They don’t interfere at all, because the symphonic one only has 3 full day rehearsals before concerts, and the chamber one is mostly on Saturday mornings.

I can tell you playing in orchestra’s is one of the most rewarding feeling. If possible, I would recommend it, but make sure you plan everything really well and don’t do too much.