Not sure what has changed, but no such thing as $15 camping here. Minimum charge was $20, and that was dry camping only. For electric and water sites we paid $35. That said, the showers were nice (and free), and the restrooms were clean. Lots of noise both day and night, but that's the tradeoff for stores and restaurants nearby. All in all a mediocre experience…. but convenient.
Slab City can be a dark and depressing place, but is also an interesting view into the human spectrum. You'll see all types of rigs, from new class A setups to people living out of their cars. Some attractions to check out are East Jesus, an artist community and Salvation Mountain, one man's lifelong project devoted to his faith. Worth a trip if you keep an open mind.