Android Lollipop is now on over 300 million android users, before the Marshmallow arrives in the near future. Google's not-quite-current operating system now accounts for 23.5 percent of active Android users, a healthy 2.5-point boost from what you saw just one month ago.
Currently, there are about 30% still on Jelly Bean, and about 38% KitKat, but it's clear that all those new devices and upgrades are starting to add up. The real question is whether or not that momentum will last.
Marshmallow is arriving relatively quickly, and shouldn't suffer from the early performance and battery life woes that kept some people from upgrading last year. If the newer release catches on quickly, Lollipop might not reach the lofty adoption rates of its predecessors.
More info: Android Developer