Preheat the oven to 350 degrees F (175 degrees C). Place crusts on a baking sheet.

Whisk sweetened condensed milk, sour cream, Key lime juice, and Key lime zest together in a bow until smooth; divide and pour into crusts, filling to the top.

Bake in the preheated oven until hot, 5 to 8 minutes. Refrigerate until thoroughly chilled, at least 1 hour. Garnish each pie with a Key lime slice and dollop of whipped cream.