155F is far too hot.
Is the fan working on it? If not make sure its not clogged up with dust, and that the 2 power connectors are connected etc.
155F is ~66C. The thermal ceiling for video cards is 105C.
Your video card is not overheating.
It's 68 degrees and would be cause for concern if that's the temperature at idle.
Yes and no.
It depends on the video card. Some video cards were TERRIBLY designed and idle at stupid temps. It also depends on the ambient temps.
My old 9800GX2 idled at 62C, even AFTER I bumped the fan speed by 10%.