Key Lime Cream Torte

1/2 cup plus 2 tablespoons Key lime juice, divided
1 box butter cake mix with pudding included
1/2 cup (1 stick) butter, softened
3 eggs
1 (14-ounce) can sweetened condensed milk
2 cups heavy whipping cream
Lime slices for garnish

Preheat oven to 350 degrees. Grease and flour two 9-inch round cake pans. Place 2 tablespoons Key lime juice in liquid measuring cup and add enough water to equal 1 cup. (Set aside remaining 1/2 cup lime juice.) In a large mixing bowl, combine cake mix, water/lime juice mixture, butter and eggs. Beat until well-combined. Pour batter into prepared pans and bake 20 to 30 minutes, or until a toothpick inserted in the center comes out clean. Cool in pans for 15 minutes, then invert onto wire racks and cool completely.
In a medium mixing bowl, combine remaining 1/2 cup Key lime juice with sweetened condensed milk. In a separate bowl, beat whipping cream until stiff. Set aside 1 cup of whipped cream: fold the rest into the condensed milk mixture.
Slice cakes in half horizontally to make 4 layers. Place 1 layer, cut side up, on serving plate. Spread with 1/3 of the filling. Repeat with second and third layers. Place fourth cake layer, cut side down, on top. Spread the reserved whipped cream on top of the torte. Refrigerate 2 to 3 hours before serving. Garnish with lime slices.