You can have the same set up, the website has an option in the downloads section to download older versions.
My installs are 100% vanilla as mentoned.
And I rested on a clean install (vm) and I posted the steps required to recreate the issue) that's enough assistance in my option.
15.2 server (upnp)
17 client
Scrape a movie into 15 servers movie library.
Add upnp source into 17 client (15 server upnp)
On 17 client
Select movies
Movies>Files>"Kodi15 Server">Video Library>"Files">Movie>File.mkv
None of the files at the end of the chain will be visible/therefore are unusable.
17 CAN read the library scraped into the 15 server, but it CANT view files on a 15 share! Big big backcompat issue!
Really very simple to test, less than 1 minute of work (maximum) but still surprised that there are no one looking at this or running 15 servers? I mean for me it just means I stop at 15, but still, that's a seriously big incompatibility, I'm surprised they aren't advising users NOT to upgrade if you run a 15 server etc!
I have no addins on my client as they clients! They pull kiosk style from my server. I'm a very busy guy, I quickly test the latest release too see if it works, it still broken, so I delete and get on with my life but tell the devs of the issue.
If they want to check it (as part of their job) cool, if not, I have my job to do, and can live with 15. But at least I gave them visibility of it. If 60 seconds of following 1 line of test is too much, cool
I don't have time to be kodi tester as I have a deadline for my own work, family, baby, level designs to complete etc.. but I provided them with a detailed description of the issue, provided replication instructions, gave examples, revisions, settings, file locations, navigations etc... if they can't click the buttons to test a reported bug with a detailed description, cool, but they must respect, neither can I!
it's not my job and everything works fine on 15, I can wait for a fix, if they are happy to roll out a borked install without testing reported bugs, cool, I advised them of the fault, I did my part and got back to my own job
... but I appreciate the bitchy accusations implying I'm porn hub or pirate