ubun2

I had the same problem, wanted to control a Ubuntu machine from another with windows and it went so slow it was almost unusable.

Searching in internet didn't helped.

I I installed XFCE in the ubuntu machine, just to try the interface, and I've notices that now it works perfectly. I suppose it must be something related to GNOME (since the software used, TightVNC and the Ubuntu Repository VNC sharing desktop).

Just try it