Place the graham crackers and brown sugar in a food processor. Process for about 1 minute. Slowly pour the melted butter and process until combined. Set aside.
Prepare the filling. Beat sweetened condensed milk and cream cheese until smooth and well combined. Scrape the sides of the bowl as needed. Add lime zest and lime juice to the mixture, mix until combined. Add cream and beat until the mixture forms stiff peaks.
Assemble the jars by adding graham cracker mixture at the bottom, layer with key lime pie filling. Add a layer of graham cracker mixture and finish with one layer of key lime pie filling. Repeat the process with the rest of the jars. Place in the refrigerator and chill for at least 4 hours.
When you are ready to serve, prepare the whipped cream by beating the cream, sugar, and vanilla to stiff peaks. Decorate the jars with whipped cream, lime slices and graham cracker crumbs. Serve.