Is there any customization in spice config to improve performance of console vga?
Not really. We usually try to have LXD provide the best performance we can.
Generally the recommendation would be to make sure your guest has the relevant drivers installed for virtio-gpu (if necessary) as that tends to be the most important step.
You can also install the spice guest agent to get things like clipboards working properly.
With lxd console i can use clipboard that is shared between host and client.
The only thing i wanted is to use console vga as vdi and it need better speed for working from remote.