I use the Park PW-3 pedal wrench. It’s got a significantly longer handle that I closely align with the chain stay, and then squeeze the handle and chain stay together like you would a pair of channel locks, and the pedal generally loosens easily. Of course I don’t overly tighten my pedals though (and have never had an issue with one unscrewing). But if the pedal is unusually tight this might be a little more difficult. Before I had the PW-3, I would use a regular 15mm open end wrench, and fit a 12-16 inch length of steel pipe over it to give me the extra length and leverage. — Dan