Because Austria uses those 2 voltages. The standard is 15kV in Germany. Germany also use 15kV and 25kV. 25kV is standard in Austria.
This is wrong. Austria uses 15kV almost everywhere. There are only two short sections south of Vienna that use 25 kV. Yes it does. You need to use the one that corresponds to the actual voltage on the wire you're driving beneath. In all Austrian routes currently in the game that means you need to use the 15kV setting.
Even if I have it set to Austria settings should have reset the breaker when I go through change over zone just outside of wiener nesault
That's not really a changeover zone, it's a neutral section. A short section of overhead wire with no electricity flowing through it. You'll see three blue diamond shaped signs. First sign warns you that the neutral section is upcoming. Second sign marks the point by which the circuit breaker should be opened. Third sign marks the place where you can close the breaker again.