The number of drawing requests to the X server done by an application has nothing to
do with its size/purpose. Also, as this is hidden by the tool kits API (in this case Qt), I can only assume what will make it better. It would help if you say whether this is about the KDE3 or KDE4 version.

Does it help to switch off the shading in the Caller/Callee map visualizations (Context menu>Visualization>Shading)?

You could try VNC or NX for better remote X experience.