I’m looking for an sleek integrated amp under $15k

That is an easy one. Not becasue it 'destroys' all the competition (lot of great amps listed in this thread.) But the Vitus house sound is something special. 

The Vitus SIA-025 Mk2 or 030 if you needed a bit more power but don't let the power rating of either fool you. These are high current amps with 1.4kv trannies.

The only integrated amps I have not owned in this thread are any of the Hagel's, the 866 or the Dart. but on the other side of the pond, Vitus is king........8-10 mo production wait, nearly no product here in the USA. Rarely come up used, rarely come up in discussion.

@petland  so you like it better than the Mola Mola?

Depends on what you mean by sleek. And how musical do you want to get?  You’ve got a nice budget. If sleek means a special old school look, unparalleled craft, stunning musicality, and flexibility because of optional DAC and phono cards, look no further than Accuphase. If sleek means more modern, simple box, Naim will do the job better than most. In between as someone else suggested, Boulder. 

Heaven 11 Billie mk2

I have the RS520 and I love it. Using the 520 DAC to resolve CD’s from an Audiolab 6000CDT. Also running The Classic by Project turntable via a MoFi Studio phono preamp to line in. It’s a fun system that easily drives a pair of Focal Vestia N4 augmented by a pair of SVS SB3000’s.