Do multiple layers slow loading time?

I run a Cesium project with 2 layers of local tiles, loaded by OpenStreetMapImageryProvider. However, around the poles there were two circular holes, which looked ugly, so I decided to add a third layer underneath, just to fill the poles. I loaded through ArcGisMapServerImageryProvider . Now the poles look cool. My question however is if that third layer slows the loading of the planet? The tiles over it are non-transparent pngs, so this layer is not visible, it's there just for the poles. Is it still loading the tiles, or , as there are other tiles over it, is cesium programmed so that it doesn't load underneath tiles?

Thanks in advance,