I have an Observium appliance running at my old work and I recall that initially I was getting some 'No Auth' graphs but after a bit of fiddling (with the guest configs) it all worked. I have not experienced issues since it has been working.

Not sure why it would be running slow. First thing I'd be checking is disk space. Also if it's a VM check that other VMs aren't robbing it's resources (if you are 'over' allocating the host's resources).