Best tube preamplifier for under $15k

Manley Labs neo Classic 300B

At least in a single ended system, the Art Audio Conductor is pretty great.  I replaced a PS Audio BHK with it and it was a noteworthy step up.  Not sure if it is the best under $15K but is fabulous and a good value at $8500.  

I am sure in a balanced system the BHK would be better, single ended though...

AR Ref 6.  I've not heard the upgraded SE version yet.  But the AR Ref 6 is a fantastic pre and you could pick one up used within your price point. 

I am with @roberjerman--I bought an SP-6 for less than $1000.00 recently and it is awesome.

Of course, the new Audio Research stuff may be better, but you will pay a lot more for them.  I would certainly audition one in my system.  They started out with the best of the best pre-amps back in the 1970's, and continue to produce better pre-amps than most.

Cheers!

Bought my ARC LS 15 back in 1995 and still using today and love it's musicality  Can't really remember,  but I think I paid less than $3,000