Hey erikhedvall,
So you are correct that it is taking up around ~15% even when not active. This is expected and highlighted in the tooltip of the global clip plane setting. The cost to render the Planar Reflection Actor comes directly from what’s currently being rendered in the level. Scenes that are triangle and draw call heavy will suffer the most performance issues when this feature is enabled because those costs don’t scale with ScreenPercentage.
You will need to exercise caution when using the Planar Reflections and be sure you have budgeted appropriately if you plan to use them.
Thank you,