Heat olive oil in a large saucepan or Dutch oven over medium heat; cook and stir onion in the hot oil until softened, 3 to 5 minutes. Add sweet potatoes and enough vegetable broth to cover sweet potatoes; bring to a boil. Reduce heat, partially cover saucepan, and simmer until sweet potatoes are tender enough to easily pierce with a fork, about 30 minutes.
Stir chipotle peppers into the sweet potato mixture.
Blend sweet potato mixture with an immersion blender until soup is smooth. Whisk heavy cream and lime juice into soup until smooth and heated through; season with salt.
Serve each portion of soup topped with 2 tablespoons sour cream and a sprinkle of cilantro.