Well, I don't think it's memory issue, considering your JVM will use up to 29GB of ram according to this:
After you updated forge to the latest rec. version, did you update all of your mods to the latest versions? I would try that, and if still crashing, probably going to need to use a process of elimination removing mods until it works, or start with none and add mods 1-2 at a time until it starts crashing.