Hi Basj and thanks for your fast reply!
I noticed that it´s not the little preview but the Visualizer of RainMeter, which you´re using too as I can see. Strange thing though, "Tiles" CPU usage is only this high, if the Visualizer is active. If I deactivate the Visualizer the CPU-usage of Tiles is minimal (~3%).
Hard to tell, if the problem lies within RainMeter or Tiles, but the CPU-usage of RainMeter is always under 0.5%! I did try different Visualizer-Plugins/Themes, but Tiles CPU-usage is always skyrocketing
Sorry for the confusion