1. Prepare the Beans: Sort through the beans and remove any debris or stones. Rinse the beans thoroughly under cold water and soak them overnight in a large water bowl. Alternatively, you can use the quick soak method by boiling them for 2 minutes and then letting them sit, covered, for an hour.
2. Sauté the Aromatics: Heat the olive oil over medium heat in a large pot or Dutch oven. Add the chopped onion, garlic, carrots, and celery. Sauté for about 8-10 minutes or until the vegetables begin to soften.
3. Add the Ham: Add the ham hock and bay leaf to the pot. Add the water and broth to a large pot if using smoked ham hock. Bring to a boil, reduce heat to a simmer, and cover. Cook for 1 hour. If you are using a ham bone, leftover ham, or smoked sausage, add them at the same time as the beans in step 5 (since they are already cooked) and add the liquids then. 
4. Drain and Rinse the Beans: Drain and rinse the soaked beans.
5. Combine Ingredients: Add the drained beans and diced tomatoes (with their juices). Add the chili powder, cumin, thyme, red pepper flakes (if using), lemon juice, salt, and pepper. Stir everything together.
6. Simmer: Bring the soup to a boil, then reduce the heat to low, cover, and simmer for 1.5 to 2 hours, or until the beans are tender. Stir occasionally and check the water level to ensure the beans are covered with liquid. Add more broth or water if needed.
7. Remove Ham Hock/Bone: Remove the ham hock or bone once the beans are tender and the soup has thickened. Shred any meat from the bone and return it to the soup. Discard the bone.
8. Season and Serve: Taste the soup and season with salt and pepper as needed. Remove the bay leaf. Serve hot and enjoy!

This traditional 15 Bean Soup with Ham is delicious on its own, but you can also serve it with a side of cornbread or crusty bread for a complete and satisfying meal.