I actually think you could get 16 slices from it. When I've made 3 layer cakes, they are really tall so the slices need to be smaller. If you're worried about the slices being too small, I would just serve them with some ice cream and/or whipped cream and fresh strawberries to make it seem bigger. I would also refrigerate the cake before you slice it, because it's much easier to slice smaller slices when the frosting is firm.
I read all the reviews on the cake, and the only real problem people had seemed to be in the heat, so make sure you keep it cool
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Good luck! Can't wait to hear the review!