What is the life expectancy of an air conditioning unit with a booster?
Sounds like your compressor is dying.  You are probably on borrowed time.  Hard to say how long it will last, because it depends on how much the unit is running (depends on climate).

A total lifespan of 15 years is reasonable for a unit before major repairs are required.

Note that newer systems are usually far more efficient (SEER and EER ratings).  And so they can pay for themselves pretty quickly.  Especially with the tax credits that are available now.