If you’re idling at 300mb with containerd running, you’re not getting better than that with a modern general-purpose distro. As others have said, switching to another vps’ free tier that offers more is your single best bet by a mile. About the only options you have on this one are compressed ramdisks being used as swapfile (zram) and literal disk swapfile to get you the rest. It’ll be very slow though if you have to load half your workload on shared platter swapfile.