San Diego to Las Vegas-Stay on 15 or use 215 to skirt LA?

2 major interchanges are 91-60 and 215 that's 1 interchange then you have the 10 and the 215 in San Bernardino.
The 215 is a little closer but when it ties in with the 60 and until you get to the 91 it is almost always very busy, and the 215 between Riverside and San Bernardino is usually busy
Also when the 215 and 15 merge if your in an RV and on the 215 you have to merge over to the slower lanes on the 15.
I live in Lake Elsinore and drive that route once or twice a month,
but not in my motorhome