I prefer to cook this soup on high because it ensures that the beans will become tender within 5 hours. You can cook this bean soup on low, but the cooking time becomes longer and more variable.
15 Bean Soup - Instant Pot
You don't need to pre-soak the beans to make pressure cooker bean soup. Simply combine the dried beans with the other ingredients listed above: 8 cups water, olive oil, onion, celery, carrot, garlic, parsley or thyme, spices and salt. Secure the lid and cook on high pressure for 40 minutes, with a natural release. Let the pressure release naturally for at least 10 minutes, or you can wait until the float valve drops on its own.
If you have a 6-quart Instant Pot, don't add more than 8 cups water or the pot will be too full.
If you want to add meat, you can add a ham hock or smoked sausage before cooking the soup. Other types of meat will get overcooked.
Total Instant Pot cooking time = 20 minutes to reach pressure + 40 minutes cooking time + 20 minute natural release