Trip Denver,Co to San diego with a stop in Las vegas

Appreciate all the help. Have a couple of questions

Do we stay on I215 thru San Bernardino to I15 or cut over to Ontario and then to I15

Someone said that the Cajon pass is bad with construction and should not be attemped on a Friday which is when we were figuring on being there on our way to Las Vegas

Having never driven in Californis ( only seen Pictures ha ha )I'm wondering how bad the traffic is on this route between Can Diego and Las Vegas