Hello
Thank you very much for sharing your results. The issue with the blurred background appears to me as something alarming, as it is true for almost all objects in the the Cosmos browser in general ! Once you move objects around 100m far from the camera textures will start to blur and loose sharpness. It becomes visible, once you scale up objects in the distance. It is easy to test, by just applying a texture to a cube and move it to the background. It can be avoided manually, setting the Blur Scale to -100% and make it sharp again. I believe this could be an undetected bug. There also is a thread on this, showcasing the trouble. See link with no statement yet.
Maybe that is also why it renders faster when changing the scene to Bitmap ? Not because it is a Bitmap, but because there is less accuracy / sharpness !
https://forum.corona-renderer.com/ LOD for Human models from the Cosmos Browser
_
This might be a bit off-topic but it could also be connected with the way Intel-chips or M-chips deal with textures.
A