You can adjust pre-render storage and render settings in Options. This is particularly useful when using embedded composite shots or using composite shots on the editor, as you can maintain fast performance regardless of the complexity of the timelines involved.
Pre-rendering creates a full quality version of a composite shot or video asset, providing faster performance. However, some intensive visual effects will always be too complex to render in real time. HitFilm uses GPU acceleration and intelligent caching to maximize performance across a wide range of hardware.