Thanks to your post I have noticed that the English version of the page is much older than Russian one.
When visiting such pages I usually cheat and open them through translate.google.com, even if I understand Russian. I am not used to reading in Azbuka and therefore I read very slowly.
15.1 is the current firmware also for PocketBook 360 and 301, but it is not as rock-stable as 14.2, so the official recommendation from PocketBook is to keep 14.2 unless you need features that 15.1 introduced.
A new, more stable firmware version was promised, and will be available "Real Soon Now" (TM).