Somehow, in all the events that surrounded the release of 15.9, sending out the actual announcement slipped through the cracks...
So here it is, a bit over a year later: cscope-15.9 has been released on 2018-07-24. This is, like usual, purely a bugfix release.
Arguably the largest single change was that in December 2017 the source was moved from CVS to git, here are SourceForge.