best gold classic watches around 15k
I find the less complications there are, the easier a watch is to read.and use. Service costs also tend to be less when you don't have a watch with complications.. I'd much rather own a Patek if I can find a good mechanical one in that price range than any other brand that's out there. Their level of detail and finishing is extremely nice benefit as well..
You would be hard-pressed to find any complicated Patek not requiring major service in that range. The addition of an annual calendar or chrono to the Calatrava/Nautilus typically increase the base cost by about 15-20K alone.
The winners in this price range I think are still Breguet Classique, VC malte as mentioned above, and possibly an AL&S Richard Lange, which I've seen just above the target price used. Although I like AP, I'm not a fan of the Jules Audemars line which would be the comparison here.
It's bit off the beaten path that leads to the default Lange / Patek selection, but for me that was part of the appeal of this H. Moser & Cie Mayu:
Love the deeply concave bezel:
The beautifully finished movement incorporates a power reserve indicator:
Here's a beautiful version in white precious metal (I don't recall which) and center sweep second hand.
I don't think you are gonna find any complicated patek's in your price range even second hand. Brand New they are closer to 50k and second hand at best 25-30k. It seems like your heart is set on a patek though.