Here's how the streams break down on average for the viewer.
Low quality video is very low-quality. 240p or 320p. Low-quality settings will use about 0.3GB (300MB) per hour.
SD quality video is standard 480p video. SD-quality video uses about 0.7GB (700MB) per hour.
HD-quality video uses about 0.9GB (720p), 1.5GB (1080p) and 3GB (2K) per hour. (this is what most congregations stream)