Between 2015 and 2016 only a few niggles were changed i think. Better rear shock (the 15's are prone to corrosion) and better CCT's on later 16 models. Both of which could of been sorted under warranty if they were issues whilst in warranty.
Nothing too major, just ironing out the problems which the earlier bikes had i think.
A couple of colour changes too.
The 2017 has a Slip & Assist clutch which feels quite nice... thats off the XSR900 i think. Also 3 traction control modes are available.. but i dno how good they are as ive not ridden one yet.