Combine carrots, scallions, garlic, ginger, curry powder, chicken broth and 2 cups water in a slow cooker. Cover and cook on low until carrots are tender, 7 to 8 hours. Remove from heat and let cool slightly. Working in batches, puree soup in a blender and return to slow cooker. Stir in heavy cream, season with salt, cover and cook until heated through, about 15 minutes longer.
Ladle hot soup into bowls and top with a dollop of yogurt and a sprinkle of cilantro, if desired. Place shrimp on top and serve.