The chances of having a serious snow problem on any of the I15 passes is pretty limited. This is a few inches of snow, if any, not feet. More likely a spin out and accident from someone who drives way too fast for conditions as opposes to a traffic slowed to a stop and sit out the storm. Very infrequently they'll close Cajon or run escorts . This is more an every couple of years thing. not several times a year. Cajon can get rough because it's got heavy commuter traffic, I40 and I15 meet in Barstow then are funneled down to the greater L.A. area. it's also an access route to some of the mountain resort areas and feeds Highway 395 which is a busy north/south Highway to the eastern side of the Sierra and north. Weekends are bad with Vegas traffic.
If weather looks to be bad, I wouldn't go west out of Death Valley on 190. That's rugged, remote country and gets to 5000 feet or so.