Slow Cooker Ground Beef and Vegetable Soup

1 (32 fluid ounce) container beef broth, or more if needed

1 pound ground sirloin beef

1 (15.25 ounce) can whole kernel corn, drained

1 (15 ounce) can green beans, drained

1 (15 ounce) can peas, drained

1 (14 ounce) can tomato sauce

3 carrots, cut into bite-size pieces

2 potatoes, peeled and cut into bite-size pieces

1 onion, chopped

1 large stalk celery, cut into bite-size pieces

1 clove garlic, minced

1 ½ tablespoons chopped fresh parsley

½ teaspoon celery seed

2 bay leaves

salt and ground black pepper to taste