15 pounds? What is that supposed to be? A joke? Please put some reasoning behind your price.
I have placed test adverts with minimal design or effort on sites such as Rediit, Bing and Facebook. They all have varying prices, with some dramatically having less than £15 in budget. On average, they were able to pull 300.935k total reach for £15, which is 20.062k reach per/£ within 2 weeks of launch. Unless your blueprints are able to push those sorts of figures, then there's really no discussion here.