These weren't inherently $15M properties - obviously price is no object for him and once he started buying adjacent properties the prices went way up. Zuckerberg paid $14 million in 2013 for a 2,600 sq ft house that was valued at $3.17 million [1]

As far as whether they're "regular people", depends on perspective. Relative to the US / world, a net worth that includes equity in a $3M+ house is an outlier but most of these people live what would have been considered a typical "upper middle class" lifestyle a couple of decades ago [source: me, ex Palo Alto resident, still have friends there]. Putting a couple of kids through college has become insanely expensive. They don't have compounds in Hawaii or fly around on private jets.

[1] https://www.sfgate.com/tech/article/Zuckerberg-to-raze-4-hou...