Most of our controls have other controls in the control templates (e.g. Chromes) which allow us to have unified look and easier styling. Because in Silverlight there is no support for Decorator pattern our Chromes are controls which have control templates and visual states. I believe that this chromes are causing the increased memory usage.
We are in the process of researching if we can reduce the memory usage.
If you need extremely optimized theme then the best approach would be to create custom theme with the smallest possible number of visual elements and visual states. Such theme is ExpressionDark where I think we are not using chrome controls.
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