Are circuits damaged by a constant 55°C environment?
The general working assumption is that life halves for every 10 degrees C rise, so you could guess the lifetime will be only 25% of the life at 25 degrees C ambient.

From your proposed operating temperature to the maximum permissible is only 15 degrees so it’s hard to actually do an accelerated test. You could try pushing the rated limits in a destructive test, but you may get an unnecessarily pessimistic number (many parts will work with relaxed specs at very high temperatures). It’s also possible to get an optimistic answer, particularly if it temporarily stops functioning, but that’s less likely.

My guess is that it would be okay for some years, but that and $2 will get you a cup of coffee. A better number could come from analyzing each component and applying reliability calculations. The LSI chip and any ceramic or tantalum capacitors are probably the weak links, and any stressed power supply components such as linear or switching regulators. 

Electrolytic capacitors often have an operating life of only 2000 or 5000 hours at rated temperature (usually 105 or 85 degrees C), so they are a typical weak link, so it’s good your camera has none.