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

highly recomend the Pathos Kratos Tube Hybrid Integrated Amplifier.  Beautiful craftmanship and incredible sound quality! One for sale below for 8K

Pathos Kratos Tube Hybrid Integrated Amplifier – Upscale Audio

Pathos Acoustics Kratos For Sale | Audiogon

The two best integrated amps I've heard at that general price point are the: Audionet Watt ($18,800) and the Mola Mola Kula ($15,055).  Honestly, nothing touches them sonically!  Since you specified $15K and below let me focus on the Mola Mola Kula.  Very transparent, 3D, dynamic, and has great bass.  For extra, you can also add a world class DAC (same as the famous Tambaqui) as well as a phono stage (same as Lupe), built-in, if you choose.

Linn Klimax DSM.  Brand new.  If not in Europe, price is even lower after subtracting VAT.

https://www.ebay.com/itm/374690462064?hash=item573d4ab970:g:UPcAAOSw~bZj66EV&amdata=enc%3AAQAIAAAAwJgJKJkKtWTE8GZ%2BsmCvj70eK2Edgdr6dsSf%2B3ZfLSjAEki%2BZIfv8uILQFs%2F0oJm%2B2bqYACt6QZfcA4UohEkhidI1J83ETadPR09Cj%2BoowvBJ0zWDsHLgwgeWhZO0QEc%2FMTZcCzAIpx0EVqvvV0Hf%2F4ctVkihR9hv93CJvI%2BBsUQ3X7PVdHgGFOdm%2B9%2BaBVS2GXDhl%2FOzFK0bJpFNX4uPSH700DmpQ551m85xdhyJE4thJnPaDV165GQlEaeTZYIJA%3D%3D%7Ctkp%3ABk9SR-DXuOaPYw

The current crop of Mola Mola amplifiers are not old technology.  They represent up to five generations beyond even the NCore module. The outlying circuitry is also unique to Mola Mola. Regardless of class of operation, they sound fantastic! 

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.