My 2015 has done this from almost day 1. I ride it five days a week, year round, and it probably happens once every week or two. At first, my dealer told me to make sure that I'm not doing it before the fueling system was fully primed, but even after making sure I wait it still happens. My dealer checked it over during its annual and couldn't find anything wrong with it (no codes/voltages are correct). I've come to the conclusion that it's just the way it's going to be until it leaves me stranded somewhere (which I hope never happens).
For those of you that have a slow or erratic starter issue! - Could you make a video (concentrating on the audio side) of the problem.
Direct the video at the engine then direct it to the starter solenoid switch ( remove the battery cover to do this ).
I have an idea as to what the problem may be but will need to hear the symptoms to be sure.