Don't know what to say, however I just switched between both versions on both cpu's and the video quality on the cpu's that run Kodi 15.2 are much better than if they were running 16.
Seems as though it has something to do with 11.iptvprivateserver.tv (used in Kodi 15.2) and portal.iptvprivateserver.tv/stalker_portal/c/index.html (used with Kodi 16)
There was a time that when I re-installed Kodi15.2 on one of the cpu's, still had the address portal.iptvprivateserver.tv/stalker_portal/c/index.html in stalker client. Channels did load, however quality was very bad....then I just entered the 11.iptvprivateserver.tv address and the quality improved.