I’ve experienced the same problem with the Kite Demo when preparing a benchmark - see here: Systematic rendering performance problem with 4.17 - Debugging, Optimization, & Profiling - Unreal Engine Forums
In 4.14, everything runs smooth. Starting with 4.15 up to 4.17 the kite demo is a “mess” when it comes to performance - as you said, an “unplayable slide show”. Maybe its the grass tool, maybe something else. My tests showed that most of the frame time is spend in the Dynamic part of the BasePass,