Just registered on this forum to give my thoughts on this. Well not really my thoughts but my evidence.
https://www.dpreview.com/reviews/image-comparison/fullscreen?attr18=lowlight&attr13_0=sony_a6300&attr13_1=fujifilm_xt1&attr13_2=fujifilm_xt2&attr13_3=nikon_d5500&attr15_0=raw&attr15_1=raw&attr15_2=raw&attr15_3=raw&attr16_0=6400&attr16_1=6400&attr16_2=6400&attr16_3=6400&attr171_0=off&normalization=full&widget=1&x=0.345942857142857&y=-0.08956372968349002
On that page you can clearly see the X-T2 has a similar amount of noise to the X-T1, maybe a little better, whilst presenting a good deal more detail.
I previously had the Sony a6300 which I was OK with shooting at ISO 12800. So it surprises me that the X-T2 is actually even better.