Heat a large skillet over medium-high heat. Cook and stir hamburger and bacon together in the hot skillet until hamburger is browned and crumbly, 7 to 10 minutes.
Stir cooked hamburger and bacon, baked beans with pork, kidney beans, lima beans, onions, ketchup, brown sugar, and mustard together in the bottom of your slow cooker.
Cook on Low until hot and thickened, at least 3 hours.