In a large bowl, gently toss together blackberries, raspberries, blueberries, and white sugar; set aside.
In a separate large bowl, combine flour, oats, brown sugar, cinnamon, and nutmeg. Cut in butter until crumbly. Press half of mixture in the bottom of a 9×13 inch pan. Cover with berries. Sprinkle remaining crumble mixture over the berries.
Bake in the preheated oven for 35 to 40 minutes, or until fruit is bubbly and topping is golden brown.
For the whipped cream, in a large mixing bowl place the whipping cream, vanilla extract, and sugar; stir to combine. Cover and chill the bowl and beaters in the refrigerator for at least 30 minutes. When chilled, beat the mixture until stiff peaks form.