I don't think that it's using by default 8GB since the 64-bit version which is used by my container uses according to the documentation a Xms configuration of 16GB, but I think the documentation is a bit outdated.   After looking further into the files it mentions that you should edit ProjectZomboid64.json in the main directory and add the parameter there:   I think something like this should do the job just fine in ProjectZomboid64.json: