I owned the higher end NFB 8, which also used the Wolfson DAC chips, as in the 15.
I found it had good weight, dynamics and definition, and was very quiet, but had the "Wolfson" sound- a bit softer on top and warmer overall, in contrast to the Sabre DACs, which are more lively and incisive. A very nice sounding DAC, but I prefer a livelier sound. I know Kingwa has a soft spot for the Wolfson.
I expect the 15 sounds a lot like the 8. If you taste is for faster and brighter, perhaps a shade more digital, maybe one of the Audio-GD Sabre models would work better, but if you prefer an easier, warmer sound the 15 may well be your cup of tea.
All of these units are very well designed and constructed. From that standpoint they are unbeatable values. I use an Eastern Electric Plus w/ Dexa op amps and simply love it.