Fifteen ounces of canned pumpkin is almost just shy of 2 cups (16 ounces would be 2 cups). A 3-pound pie pumpkin will likely give you enough puree for your recipe. Here are some good tips for using fresh pumpkin:
Pumpkin math: After cooking and draining, this is about what to expect from a typical cooking pumpkin.
2 1/2- lb.pie pumpkin =1-3/4 cups puree
3 1/2-lb.pie pumpkin =2-1/2 cups puree
6-lb. carving pumpkin=2-3/4 cups puree
5-lb. round=3-1/3 cups puree
Pumpkin storage: Puree can be refrigerated in a tightly sealed container up to 3 days or stored in the freezer up to 6 months.
Cooking Fresh Pumpkin Puree
Prep: 50 minutes Roast: 1 hour Stand: 1 hour Oven: 375°
1. Preheat oven to 375°F. Scrub pumpkins thoroughly. Cut pumpkins in 5-inch-square pieces, discarding stems. Remove seeds and fibrous strings (save seeds for roasting, if desired). Arrange pumpkin pieces in a single layer, skin side up, in a foil-lined shallow baking pan.
2. Roast, covered, for 1 to 1-1/2 hours or until tender. When cool enough to handle, scoop pulp from rind. Place, in batches if necessary, in a blender container or food processor bowl. Cover and blend or process until smooth (or for a chunkier puree, blend or process until slightly chunky).
3. Place puree in a 100% cotton cheesecloth-lined fine mesh sieve (use a double thickness of cheesecloth). Allow to stand for 1 hour to drain. Press lightly to remove any additional liquid (discard liquid).