I dont know if this is good/normal but for whatever reason i had a default Java Argument in my PATH Variables which overrid anything i changed in the java arguments of forge.
It was set to 256mb i just changed that to 12G which i wanted to use for minecraft. I know this will cause Problems at some point but i don't know if removing it is a good thing either.
You can check if you search for "PATH" in the windows start menu an then pressing the "enviroment Variables" button under System varibals could be "_JAVA_OPTIONS" if this is set -Xmx[something] this could cause your Problem.
I don't know what could happen if you manually add this, therefore I DO NOT Recommend adding it, but if there is variable present this could be the cause.