In case anyone is trying to play with this app...
I found essentially two primary issues with interactive performance (not load performance).
1. The animations. When you click on a person in the tree, several animations are performed which consume a good part of the 7 seconds mentioned by elyoh. These are most easily disabled by looking for constants named '*Duration' and setting them to zero,
e.g. "NodeFadeInDuration" in Diagram.cs.
2. Constantly maintaining the "Family Data" views behind the scenes. The "Family Data" views are accessed when clicking the 'Expand' button over on the right-hand side. The "Family Data" views cannot be seen simultaneously with the chart, yet a lot of work
goes on to update the data for those views as the user moves between people. This extra work is most easily disabled by commenting out the 'guts' of the function OnFamilyContentChanged in the file FamilyData.xaml.cs. If you do so, those views don't change:
extra work would need to be done to build the views when the 'Expand' button is clicked.
The size of the tree would have a definite impact on interactive performance, mostly due to the second issue.