Hard to believe you would be having trouble with a 50 amp service simply by using a 1500 watt heater. Are you tripping the park 50 amp breaker? Or are you tripping one of your inside breakers?
As mentioned, the 50 amp service is actually two legs of 50 amps each giving a total of 100 amps.
If you are tripping an internal breaker, then you may be loading that one breaker too much. Likely multiple outlets and/or other devices are connected to each breaker in your panel. Try the heater in different outlets and see if you still have a problem.
We can run two ACs, the microwave, water heater on electric, and the clothes dryer on 50 amps with no problem. And when it is cold we can run a heater, the electric fireplace, the same microwave/water heater/dryer and still have no problem.
