Route 15 Begins at the Four Level Interchange based intersection in Murrieta Heights where it is cosigned with Interstate 4 as the Olympic Freeway transitions to the Palomino Freeway. Route 15 heads in a northeastern direction and the freeway narrows to a four lane divided freeway flanked on opposite sides by the Tataviam Mountains to the north and the Palomino Highlands to the south. Its first intersection is a T-shaped cloverleaf with Sustancia Road. Immediately after this junction, Interstate 4 losses its concurrency with Route 15. The median widens as well to accommodate a large rest area which houses an Ammu-Nation and a RON gas station with a 24/7 and Bishop's Chicken. The highway curves along the eastern footing of the Tataviam Mountains for most of its routing. Route 15's second and final intersection is another T-shaped cloverleaf with Senora Way. The route continues in a northwest direction as it and Interstate 4 merge end and merge into North Interstate 1 and Route 13, forming the Senora Freeway. The intersection with the two other routes mark the end of Interstate 4/Route 15 and the Palomino Freeway.
|Tataviam Mountains||Senora Way/|
|Grand Senora Desert||Sandy Shoresnorth -|
- Given the rural and mountainous nature of the Palomino Freeway's general position it is hard to pinpoint the definitive inspiration for Route 15. Route 15's close proximity to the Tataviam Mountains may make it based on California State Route 2 in position, Interstate 210/State Route 210 for being a freeway that runs parallel to the San Gabriel Mountains (part of the Tataviam Mountains' inspiration), and parts of Interstate 10 that run through the San Gorgonio Pass between the San Gabriel and San Jacinto Mountains.