Heat oil in heavy large pot over medium-high heat. Add carrots and leeks; sauté until leeks begin to soften but not brown, about 5 minutes. Add garlic; sauté 1 minute. Add cumin and crushed red pepper; sauté 30 seconds longer. Add 6 1/2 cups chicken broth. Bring to boil. Reduce heat and simmer uncovered until vegetables are very tender, about 35 minutes.

Working in batches, puree soup in blender until smooth. Transfer soup to large bowl. Cool. Whisk in 6 tablespoons sour cream. Cover soup and refrigerate until cold, at least 4 hours or overnight.

Stir lime juice into soup. Thin soup with more broth, if desired. Season with salt and pepper. Ladle into 4 bowls. Spoon 1/2 tablespoon sour cream atop each serving. Sprinkle with cilantro and lime peel.