Line the springform base with parchment. Mix graham crumbs and melted butter and press firmly across the bottom and slightly up the sides.
Chill the crust for 30 minutes while making the filling. Beat softened cream cheese and powdered sugar until completely smooth.
Gradually beat in Key lime juice, lime zest, and vanilla. Scrape the bowl to ensure citrus and cheese are evenly blended.
Whip cold heavy cream in a separate bowl to stiff peaks. Stop before the cream becomes grainy or begins separating.
Fold one-third of the whipped cream into the cheese mixture, then fold in the remaining cream gently to preserve its volume.
Spoon into the cold crust and smooth the surface. Cover and refrigerate at least 8 hours, preferably overnight, without disturbing the pan.
Run a thin knife around the inside edge before releasing the springform ring. Keep the cheesecake cold while preparing to serve.
Slice with a warm wiped knife and lift with a broad server. Add thin lime slices at serving time if desired, removing them before eating.
