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.
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...