You can switch on the client side to high color (16 bit), but not low color (8 bit). You can also enable JPEG compression. With both of these options in sessions, the speed for me is from completely unusable (~ 45 seconds for the initial drawing of the screen and ~ 5 seconds lagging when you click on the menu) to completely usable (<5s for the initial drawing of the screen and <1s lag when pressing the menu) .
Please note that this is the time to connect from a remote computer to my home iMac on a cable modem. In addition, it works with two screens that are sent, although I use only the main VNC channel. I have yet to figure out a way to disable the secondary screen in VNC and its problem in order to disable it.
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