Disable Viewport Rendering

1. If you don't need to see your Unreal Viewport then it is best to disable it while live-streaming. This will still give you control over your content via the Editor but without rendering both you viewport and your OWL Cinecam output.
2. You can do this in-Editor and at-Runtime by using the toggle boxes in the Off World Live Editor drop-down:
3. Your performance gain will depend on the resolution of your screen and your Viewport screen percentage setting, but it can be between 25-50% FPS increase.

Reduce Viewport Rendering

If you need to see your Viewport, there are alternative options which keep it on but reduce how much GPU it uses:

1. The best is to switch on DLSS (see guide here). This will render at a lower resolution but upsample and so use less GPU. It also works on the OWL Cinecam output (only at-Runtime) creating double the performance gains:
2. If you don't have an RTX Nvidia GPU the you can reduce your Viewport resolution in 'Viewport Options' by changing your Screen Percentage to 50%:
3. You can also set your Viewport to Brush Wireframe in the 'View Mode' dropdown which will reduce GPU consumption but allow a basic view of scene objects: