Combine graham cracker crumbs, sugar and butter together and press firmly into the bottom of an 8" or 9" springform pan and about 1" up the sides.
In a large bowl, beat cream cheese with an electric mixer until smooth and creamy. Add in sugar, key lime juice, lime zest and vanilla and beat until smooth.
Add heavy cream and beat on low speed until incorporated, then beat on high speed until thickened and fluffy with stiff peaks.
Spread the cheesecake filling into the prepared pan, cover and refrigerate for at least 5-6 hours or until firm. Slice and serve with sweetened whipped cream if desired. Enjoy!
Notes
If you can't find Key Limes, you can use half lemon juice and half lime juice.