You could do a search on eBay of Completed Items to find a price and Facebook Marketplace is a good indicator. 15Ks are quite popular and they are not heavy, except when compared to modern machines with plastic parts that don't last as long. Is it still in a treadle or some sort of base? Some charity shops take them, or sell on Gumtree, Facebook Marketplace, Freegle, etc. Do you have any local vintage machine repair shops, they might be interested. Replacement feet can be can be bought. I hope you can find a good home for it; they are worth while rescuing, if only as parts machines. Singer made all their own screws so some are quite hard to find.