Hi Kay,
Thanks for reaching out. You are correct that our build hasn't been publishing to Maven central. We're aware of the issue and a colleague of mine just confirmed that he will prioritize looking into it.
In the meantime, the functional and API difference between v2.15 and the version which has been humming along on our production servers isn't large, so I believe you should be able to safely use 2.15 now, then upgrade at your convenience when the build process is fixed. The most significant delta between 2.15 and the latest appears to be some new syntactic sugar available for NFTypeSerializer declarations, plus some new features contributed from externally to help with convenient HeapFriendlyHashMap usage.
Thanks again,
Drew.