Hi, Vadim!
It seems that your particular issue is not the one described in https://jira.jboss.org/jira/browse/JBIDE-6039. (But I suppose that JBIDE-6039 also plays significant role in your problem).
The problem is that we calculate Javadoc info for each proposal using a long running JavadocContentAccess2 methods. But this is not a proper place for such calculations. This issue is subject to be fixed in JBossTools 3.1.1.
It will be greate if you would verify this issue after fixing.
I'll let you know in this thread.