It's frequently an indication of a malfunctioning, faulty or uncalibrated thermostat when a commercial oven doesn't achieve the correct temperature quickly enough or gets too hot. You will need a professional to check for an effectively calibrated thermostat. If the flame dies before reaching temperature, or if there is a temperature variation of 5-10 degrees, your thermostat has to be adjusted. Calibration should always be done by a trained expert.