Public parks with pavilion rentals are criminally underrated for this budget - most cities charge $50-300 to use a covered shelter, which leaves you plenty for catering and flowers. The key thing people miss is that you can transform a basic pavilion with cheap string lights and potted plants (which you could propagate yourself beforehand if you're into gardening like I am), and it photographs beautifully without looking sparse. I'd also suggest checking if any local nonprofits, churches, or community centers rent their halls for weddings - they're often $500-1500 and come with built-in tables and kitchens, which cuts down on rental costs dramatically. With $15k for 80 guests, you're looking at roughly $185 per person if the venue takes a chunk, so finding something under $1k for the space itself really does make a difference in what you can do with food and flowers.