Many factors can impact the performance of your project before it ever gets streamed to the web client. How you optimize things within Unity or Unreal will largely come down to the design of your experience and the needs of your users during the event / interaction.
Some quick optimization tips include:
- Disable motion blur
- Disable raytracing if possible
- Enable hardware encoding for full motion video (FMV)
- Turn off the in-game mouse pointer
For more details on what factors may impact the performance of your game click here.