As a born and raised native Southern Californian that I am, I too would highly recommend continuing to commute the northbound I-15 route over the I-215 from the San Diego area as the majority have posted...
The worst of the I-215 route that I can confirm is thru Riverside, which has mainly been a snarled mess along the I-215 CA 60 CA 91 interchange, the second worse portion is next going thru the heart of San Bernardino with the potential of dealing with more heavy traffic (but not always), minus one lane that I remembered in my heydays there when that route was known as the temporary I-15e.
In February 1998 upon visiting while in Palm Springs, it was moderate to light heavy traffic on the I-215 in San Bernardino between the I-10 and Devore while driving to Las Vegas on a Friday night, I couldn't believe it.
In it's usual state, when the I-215 meets with the CA 60, it becomes a junction route for about 5 miles or so between Riverside and Sunnymead (which they call Moreno Valley now) in which traffic flow thru this stretch could be ok, slow, or pure gridlock at any given moment.
Commuting on the northbound I-215 route is still doable, however there is a much greater chance a commuter will be tied up in traffic versus the northbound I-15 if the location option element is there.
April 2009 - westbound CA 60 and I-215 with light moderate traffic approaching Riverside :
This picture I taken is a rare sight at the westbound CA 60 I-215 and CA 91 interchange without the usual 100 to 250 vehicles fighting for position that I endured in the past during daytime commutes in my heyday :
I cannot speak for the I-15 corridor of what it is like now between Corona and Escondido as I have not commuted thru there since 1978, however during my one day Anaheim visit in 2009 I drove to Las Vegas the following day which was during rush hour on a Friday morning...
Reached the eastbound CA 91 at I-15 interchange at Corona - 700am :
Smooth light traffic on the northbound I-15 at CA 60 interchange crossing here 8 minutes later :
Smooth light traffic on the northbound I-15 at I-10 interchange crossing here 5 minutes after :
Overlooking in south direction at the north ending of I-215 where it meets with I-15 in Devore at 723am :
Unless some sig alert has been issued, it's pretty hard to beat reaching Devore in less than 30 minutes from Corona that's virtually a hassle free route in Southern California while avoiding both Riverside and San Bernardino going in the same northbound direction before heading on to Cajon Pass.
Happy travels.
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