O2 sensor on 96 sentra

I have a 96 sentra. The check engine light came on, I took it to Autozone to check the code and clear it. I was told it was the rear bank O2 sensor. It appears there are two O2 sensors on my car, one right in the front by the engine and another by the cat convertor. How long do O2 sensors last? I have ~150K on my car. Should I just replace both? Also I have been driving around for several days and the check engine light has not returned, so does this sensor even need to be replaced? Another question maybe not related to the O2 sensor, sometimes when I start my car it hesitates, like it's being flooded with gas. I have to floor the car to turn off the injectors to get the car started. Is this the same problem or different?

its different, the rear o2 sensor is a catalyst efficiency monitor and does nothing for your car but tell it if the cat is working

probably the CEL is a result of a different issue that is causing too much gas to be injected, thus fouling up the spark plugs, cat, and oxygen sensors. i would make an attempt to figure out and fix your driveability problem or else you may be stuck replacing both 02 sensors and the cat more than once.