In a medium bowl, combine graham cracker crumbs, sugar, and melted unsalted butter until moistened. Press into a 9-inch pie dish. Freeze for 15 minutes.

Whip the heavy cream on medium-high speed until stiff peaks form, about 2-3 minutes. Set aside.

Blend softened cream cheese and sweetened condensed milk on medium speed until smooth, about 1-2 minutes.

Add lemon zest, key lime zest, vanilla extract, sour cream, lemon juice, and key lime juice. Mix on low speed until well incorporated, about 1 minute.

Gently fold in the whipped cream until just combined to maintain an airy texture.

Pour the filling into the chilled crust and smooth the top. Cover with plastic wrap and refrigerate for at least 2 hours.

Once set, whip remaining heavy cream until soft peaks form and dollop on top. Garnish with lemon and lime slices.