I agree, that something must be wrong with your VM install. The asterisk I have at home is running on a super old machine with only 128MB and I still have 50% memory left with all services running. I have also done VM install on the amazon EC2 micro instance (512MB) and there are no memory issues on it either, plenty of memory left.
ok just to let you know.
I redid the installation without the yum update.
so Asterisk version is 11.2
no memory issue.
So I am wondering whether this comes from the yum update which upgraded to 11.6 or is this comes from subsequent modules installation like freepbx framework and such.