Preheat the oven to 350°F.
In a stand mixer, beat 3 packages of softened cream cheese and 1 1/2 cups of packed brown sugar on medium speed for about 5 minutes until light and fluffy, scraping the bowl as needed.
In a separate bowl, whisk together 15 ounces of pumpkin pie mix, 4 large eggs, 1/4 cup of sour cream, 2 tablespoons of flour, 2 teaspoons of pumpkin pie spice, 1/4 teaspoon of salt, and 1 tablespoon of vanilla until combined.
Gradually mix the pumpkin mixture into the cream cheese mixture on low speed until blended.
Pour the filling into the pre-baked crust and bake for about 1 hour, until slightly wobbly in the center.
Turn off the oven, prop the door open with a wooden spoon, and let the cheesecake sit for 45 minutes.
After cooling, cover with plastic wrap and refrigerate for at least 4 hours or overnight.
To serve, run a blunt knife around the edges of the cheesecake before removing it from the springform pan and add desired toppings.