I've had some pretty tight pedals, and even with a 12+" long pedal wrench and good wrench flats, they were a bear to remove. You might want to soak that joint with a penetrating oil to chemically loosen the screw. Try to use a good quality hex bit, like the one suggested above with a breaker bar. Don't damage the pedal socket. Also, I find it helpful to wear gloves, so when it does break loose, your hand isn't impaled on the chainring.
When reinstalling the pedals, use plenty of grease on the threads and no ned to use gorilla strength torque. Remember, when pedalling, the rotation is in the direction of tightening.
PS - I wish all pedals have wrench flats.