If you want to share your webcam: Deactivate webcam sharing by clicking on the camera symbol below. Click on it again to activate sharing. A window should now appear where you can select the quality. Select "Low" and then click on "Start sharing".
If that's not enough: Click on the three dots in the top right and then on "Open settings". Under "Data saving mode" you can choose whether you want to deactivate other people's webcams or screen sharing.