In a small bowl, combine graham cracker crumbs, sugar, and kosher salt. Add melted butter, then stir until the mixture begins to stick together.
In the bowl of a stand mixer fitted with whisk attachment, whip heavy cream on medium-high speed until stiff peaks form. Use a spatula to transfer the cream to another bowl, then switch out the whisk attachment with the paddle attachment.
Add sweetened condensed milk along with room temperature cream cheese, then beat on medium speed at first until light and fluffy, gradually increasing to medium speed. Beat. Turn the mixer off, then add vanilla extract, fresh lime juice, and lime zest.
Add whipped cream to the cream cheese mixture, then gently fold with a spatula until thoroughly combined.
Spoon the graham cracker crumbs along the bottom of a baking dish, enough to evenly cover the bottom. Add the key lime mixture on top, then use an offset spatula to spread into an even layer. Top with another graham cracker filling. Repeat. Enjoy!