I already answered to this question in your other thread. However, I will paste the same answer here so that it may help others from the community.
I can see that you have completely predefined the ControlTemplate of the RadDiagramShape. You need to keep in mind that such tremendous changes are out of our support scope. This means that the performance and the optimizations over those shapes is up to you.
Let me give you some tips about your current implementation of the MVVM approach. In order to stick to that approach you should not hold any visual elements in your ViewModels. You should hold the information based on which you will be able to create the UI. For example instead of saving property of type Brush, you can save property of type string and preserve only the HEX code of the color. Also, saving Image is bad practice. You can save only the path to that image and achieve the same result. This also may improve the performance of your application.
Pavel R. Pavlov
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