It is not necessarily bad if Proxmox shows high RAM usage, because the Hypervisor cannot see how much RAM the VM actually needs. Since Linux (and most OSes these days) use their free RAM as cache, it might appear 'from the outside' that the RAM usage is very high.
You could try to install the qemu guest agent inside the VM and enable it in the VM options. RAM ballooning could also be an option (needs the guest agent too).