Check book value on the GTO. Then see what Camaros similar to that are selli.g for, NOT what they are listed for. Its really hard to put a firm value on it just from seeing pictures. (not that I am the expert on value, not even close....)
I'd agree -- it's not worth much -- it needs a complete do over.... And not trying to be harsh or a smartass here. It's just a very ordinary "another" 69 Camaro and there is no shortage of 'em in this style and condition. The buyers in this market are buying "projects" and there's not many buyers out there.... and lots and lots of sellers.
I think it also depends on how many of the little pieces that you can't really see in photos are reusable, and would just need to be cleaned up a little. If someone sees it and wants to use it as a driver, it might be worth the 15k, but everyone around here is going to look at that car and think of it as a candidate for a ground up build, where most of the parts on it aren't going to be reused, and can't be sold for much.