Bring a pot of water to a boil; cook sausage in the boiling water until partially cooked, about 5 minutes. Remove sausage from water and slice.
Heat a large skillet over medium-high heat. Cook and stir ground turkey, onion, and garlic in the hot skillet until browned and crumbly, 5 to 7 minutes; drain and discard grease. Stir sausage, tomato sauce, chopped tomatoes, tomato paste, sugar, oregano, basil, and parsley into ground turkey; bring to a boil, stirring frequently. Reduce heat and simmer, stirring occasionally, until flavors have blended and sausage is fully cooked, about 1 hour.
Bring a large pot of lightly salted water to a boil. Cook spaghetti in the boiling water, stirring occasionally until cooked through but firm to the bite, about 12 minutes. Drain and transfer spaghetti to a serving bowl; top with sauce. Toss to coat.