Today I played a Kawai K15 ATX3 L and also liked it very much!
The action felt nicer and more premium/expensive with less friction than the Yamaha and it also sounded "bigger", with a deeper base and a clearer tone, but it was also louder and pp(p) playing wasn't as easy as on the B1 but still possible. The action felt responsive and quick. I like that the Silent System of the Yamaha just a tiny tiny bit more, but both are excellent imo. There is no K15 Aures, so if I want Transacoustic I must go with Yamaha.
I also played the NV5S again and imo the K15 and B1 sound much better than the NV5S with speakers. The NV5S sound really good for a digital piano - but that's it. And somehow the action in the NV5S felt more sluggish and slow than both the K15 action and the Millennium 3 actions in the K200/300.
I've recorded some Videos of the K15, the NV5S and the B1 - two Pieces, "One Summer's Day" from Joe Hisaishi and "Gymnopedie No. 1" from Erik Satie. These are just spontaneous smartphone recordings.
Sorry for the mistakes. Especially when playing the Yamaha B1 my hands were still cold from outside and the playing of the other person distracted me a bit.
Joe Hisaishi - One Summer's Day:
Kawai K15:
https://youtu.be/w2vSv5eyhAo
Yamaha B1:
https://youtu.be/2Bjujje-y44
Kawai NV5S:
https://youtu.be/asXYrwuS9GI
I will upload the Gymnopedie Videos later.