I have a multi-machine setup working on Windows of FMS13, but not sure how much help this will be. I wish there was a useful troubleshooting guide as well as an explanation on how the machines interact in a multi-machine setup.
I had a similar issue getting it to work "out of the box", I tried opening a case but apparently support is unable to troubleshoot configurations which are running other services (in my case I was running Coldfusion on the same box).
In the end, I got it working by running through the installer several times after reading articles for several days, but in particular the one by Nicholas Orr over at Goya (http://www.goya.com.au/blog/two-machine-filemaker-server-installs-and-dns-issues). Also good for reference are ports used by Filemaker (from some brilliant guys at Six Fried Rice): http://http://sixfriedrice.com/wp/filemaker-firewall/ and slightly harder to interpret from Filemaker themselves: http://help.filemaker.com/app/answers/detail/a_id/14402/~/ports-used-by-filemaker-server
I interpreted the reverse-dns issue (Goya article) to be a variation of my issue. Since I was using service bindings to keep IIS, ColdFusion and Web Direct playing peacefully together on the same machine, I needed to make sure connections between the servers for Filemaker Web Publishing used the proper service binding name.
I'm not sure how common multi-machine is, but very excited to see if anyone can provide something more concrete.
Unfortunately I can't speak to your issue, but I'd like to bring your attention to the FMS15 server specs for Windows Server 2012 R2:
From the server tech specs page at http://www.filemaker.com/products/filemaker-server/server-15-specifications.html
"Windows Server 2012 R2 Standard Edition with Update (see Microsoft KB 2919355)"
Thanks Both for replies.
It still a problem, and yes my IT team were aware of the Microsoft update to Windows Server which they did and the server specs. We've done things by the book but still can't access the admin console and FileMaker support have not resolved the problem yet, which does not leave me with much confidence on trying to attempt to reinstall it.