Preheat your oven to 325°F. Grease a 9-inch springform pan and wrap it with a double thickness of heavy-duty foil to prevent leaks.
In a large bowl, mix the crushed gingersnap cookies, 2 teaspoons of orange zest, and melted butter. Press the mixture onto the bottom and 2 inches up the sides of the prepared pan.
In a large saucepan, combine the orange juice and sliced gingerroot. Bring to a boil, then reduce heat and simmer until the mixture is syrupy and reduced to about 3 tablespoons. Strain and discard the ginger.
In a large bowl, beat the cream cheese and sugar until smooth. Add the ginger syrup, melted white chocolate, vanilla extract, and remaining orange zest, and mix well. Gradually add the beaten eggs, mixing on low speed just until combined. Pour the filling into the crust.
Place the springform pan in a large baking pan, and add 1 inch of hot water to the larger pan. Bake for 70-80 minutes or until the center is just set and the top appears dull. Remove the springform pan from the water bath and foil, and let it cool on a wire rack for 10 minutes. Carefully run a knife around the edge to loosen, and cool for an additional hour. Refrigerate overnight.
To make the candied orange slices, combine the water and sugar in a large skillet. Cook and stir over medium heat until the sugar is completely dissolved. Add the orange slices and bring to a boil. Reduce the heat and simmer for 45 minutes, or until the slices are translucent. Drain the oranges on a wire rack and arrange them in a single layer on waxed paper to dry.
Remove the sides of the springform pan. Top the cheesecake with the candied orange slices. Store any leftovers in the refrigerator.