Warm olive oil in medium skillet over medium heat. Add half of garlic and cook until fragrant, stirring, about 30 seconds. Scrape into slow cooker and stir in tomatoes, 3/4 tsp. salt and oregano.
Combine turkey, sausage, bread crumbs, cheese, eggs, parsley, remaining garlic and 1 tsp. salt in a large mixing bowl. Blend ingredients with your hands. Form into 2-inch balls and place in slow cooker. Spoon tomatoes over meatballs to cover.
Cover and cook on low until cooked through, 4 to 5 hours.