If you can access via SSH you could use port forwarding and only start the vncserver when you access the device.
Alternatively see help for port/password
osmc@osmc-vero4k:~$ aml-vnc -h
aml-server [parameters]
-f <device> - Framebuffer device
-h - Print this help
-p <password> - Password to access server
-R <host:port> - Host for reverse connection