You're paying board. You should be able to dictate your horse's care. 15 lbs of hay is barely enough for a 15h air fern of a horse (extremely easy keeper). If it's their Blue Seal feed, they should be more than willing to swap out more expensive feed for cheaper hay and hay cubes...
This is why I don't board anymore. I only found one place that would listen to me and do what *I* said for my horses (and they had private paddocks). I stayed there as long as I could, before we bought our small property. The place had only a small arena, round pen, no barn stalls for use, no covered arena, no wash racks, etc., but they fed as much high quality
hay as I wanted my horses to have and actually fed exactly what I wanted them to eat. That and the private paddocks with shelters was worth more to me than any fancy boarding stable around (and yes, we do have some very well equipped places). I searched for a long time before I found it, and was on a waiting list for 6 months to get in, but it was well worth it. It ended up not even costing me as much as the fancier barns, so that was definitely a plus
Anyhow, good luck in whatever you decide to do. Just remember to keep it simple. We can make feeding horses as complex and difficult as we want, but the horse's digestive system is simple. So simple works better!