iMac login screen is very slow (Mojave) Whenever I wake up my iMac, the login screen takes very long time to respond (roughly 8 seconds). This happens on Mojave (I cannot remember if it also happened in the previous OS but I think it did). 

I emphasize that it does not happen on my MacBook Pro which is the same OS Mojave. Therefore I think it's an iMac issue. 

What can fix this issue?
Is the iMac an older model with a hard disk instead of an SSD? It takes a while for hard drives to 'spin up' compared to an SSD in a newer MacBook Pro.