Currently, public sub counts are abbreviated in most but not all places across YouTube. In August, we’ll make this more consistent by always showing abbreviated sub counts publicly. Creators: You’ll still see your full sub count in Studio! Learn more → http://yt.be/help/abbrev-count …pic.twitter.com/pmaKk4EU4k
Ok so in your example here 15,423,627 gets rounded to 15M So basically what you're saying is until enough subs are gained to round up to 16M, the other 423,627 people don't matter...