Best $10-15K bookshelf speaker?

$10-$15K for a bookshelf? With that budget, I would start with the Alta Alyssa at $5K (passive) and force myself to justify spending more. You could have a whole Linn system on that budget. If going for a bookshelf, I would make it a 2.1 system and add a sub. For the same money, you could have Buchardt A500 Signature actives with two Purify long-throw drivers and pair it with a T+A streamer-DAC-preamp-headphone amp and call it done, and have change left over.

Dynaudio Confidence 20 or

Borreson 

Be cautious with Borreson and Raidho.  They don't work in every space.  You need minimum 9' between the speakers and typically 3-5' behind them or the glorious image that you are paying for will not come together.  Incredible speakers in the right space, a huge disappointment in the wrong space.  Note how they setup at shows.  That is not accidental.  

I would look at TAD, Marten and I think Vimberg might fall in this price range.  They are the best designed products in this price range IMO.  

Fully disclosure, I am a Raidho dealer but have no relationship with any of the other brands I have mentioned.  They are just good products.  It is funny that I really have nothing in that price range.  The Audiovectors and Wilson Benesch fall just below with stands

Hands down Vimberg Amea

I just bought a pair of YG Acoustics Tor loudspeakers. They sound amazing and look amazing (my wife has STRONG feelings about speaker size). The Tor speakers are in your price band and work well with a range of amps, and in a variety of rooms -- they are 88 db, 7 Ohm sealed-box speakers (with a minimum impedance of 3.5 Ohms). I have a REL S-510 sub as well, and they blend perfectly. Reach out to Bill at GTT Audio. He's great.

https://www.yg-acoustics.com/products/tor/