Yes, $15,000 USD seems way to high even for one in extremely nice condition. We are talking about a 31 year old 26 footer with mediocre sailing ability. I would expect a boat like that to be well under $10K USD. In that price range a boat with a new inboard engine means that the owner has more in the boat than its worth in any kind of fair and balanced marketplace.
I am not sure that buying a beat up sistership makes any more sense though. You can expect to find some ''issues'' with any boat this age. Unless very well maintained and updated by a previous owner, you might expect to need to address some combination of the following items, and in the worst case these can easily exceed several times over the value of the boat fixed up.
∑ Sails, chainplates, mast step and associated suporting structure, standing and running rigging that are beyond their useful lifespan,
∑ an engine that is in need of rebuild or replacement,
∑ worn out or out of date deck, galley, and head hardware,
∑ worn out upholstery,
∑ electronics that are non operational, or in need of updating,
∑ electrical and plumbing systems that need repairs, upgrades to modern standards or replacement.
∑ Blister, fatigue, rudder, hull deck joint or deck coring problems
∑ Keel bolt replacement (bolt on keel) or delamination of the hull from the ballast for a glassed in keel.
∑ And perhaps a whole range of aesthetic issues.