There really isn't one. The 15 goes go a long stretch with no cities alongside until you hit Hesperia.
Rochester, CA is a halfway point between LA and Victorville.
Franklin, KY
Provo, Utah is about nine hours into a sixteen hour drive, traffic and weather conditions permitting.
Acebedo, CA is the halfway point.
The city that is the halfway point between Downey, California and San Francisco, California is Acebedo, California. It is the exact geographical halfway point.
If you are looking for a major city that is somewhat in the middle, Escondido would be your closest pick. Pull out a map to see.
Independence, California is about the halfway point.
Kettleman Station, California
The halfway point between Sydney, Australia and Los Angeles, California is London, Kiribati. The closest major city that is roughly halfway is Honolulu, Hawaii.
Gallup, New Mexico is about halfway.
Morro bay
Fresno, ca