What is a fast way to get informed, when new Avast version is available? Avast own alerter can take many days. So, is there for example RSS-feed for Avast program update (i have not found one), or some other way.
There is the avast blog which has reported the avast 2015 version, you could get an RSS feed for that, but it isn't exclusively related to program releases so you would have other developments/security/interesting blog entries.
The Program Updates are spread over a cycle of two or three weeks, this is to spread the load on the update servers. With in excess of 200 million users they all can't update at the same time - that is why you aren't seeing it immediately.
Monitoring the avast forum you will get early notice of an impending program update when the beta phase starts.