It depends entirely on the condition and your location. Although the 15-80 was not one of the common submodels of the 15 class, they're still too common to really be worth anything much as collectables. Here in the US, if the machine is in perfect working order, fully serviced and still has very good or excellent decals, it might fetch around $100 on eBay (prices on eBay are usually high). If it needs a checkup at a sewing machine shop, it's probably not going to sell for much anywhere.
On the plus side, these are excellent machines when in good working order. It has worth as a nearly indestructible sewing machine, just not much as a collector's item.
On the plus side, these are excellent machines when in good working order. It has worth as a nearly indestructible sewing machine, just not much as a collector's item.