Huh, made with Vue/Vuex + map via VueLayers (OpenLayers wrapper). Actual radar data is coming from a geoserver at https://preview-opengeo.ncep.noaa.gov/geoserver/

AGOL (ArcGIS Online) is only providing the basemap and layer overlays (state boundaries etc), those probably come from Esri's "public" data portal and I doubt are part of the bandwidth issue.