Big surprise but famous big Android percentage still have old boy KitKat (4.4) – 38.9% of all Android based devices. In second place all versions of Jelly Bean (4.1 – 4.3) amounting to 30.2 percent and after that going Android Lollipop.
More than this – some hardcore geeks still use Froyo (2.3 version !!!) with 0.2% market size. And against the background of this Google release the new version even more crushing market Android devices.
So, I think Marshmallow take minimum one year after release for make same 20% of market Android device.
Here full statistic about Android usage by version as of October 2015.