> What is the tallest gearing anyone here has tried?

32 on the rear is pretty common. 30 is generally seen as too tall, and 15 on
the front doesn't have enough clearance to be safe. Sounds mostly like you just
need to get used to the bike. It's buzzy and will sound wound out when in it's
happy range. If you change the gearing too much, you'll have a hard time
reaching top speed.