Assuming this is a CE deployment, not K8S.
I suggest you update to 4.3.1. Or if you wait a few days, 4.4.0 is coming out.
2GB is the minimal memory, but the services may need more RAM depending on your application. The only way to really know is to benchmark your exact requirements until you find the right amount of RAM. It may also depend what other services you are running... for example is LDAP running on the same server? Are you running any interception scripts? Is it possible that the interception scripts have a memory leak?