When you installed kodi 15.2, it also installs the official repo. You should be able to got to Settings / ADDONS / install from repository / scroll down to Kodi repo / scroll down to subtitles. Select open subtitles .org and install.
Then you go back to /settings /videos / subtitles / select...
For both of you. Zero cache will not work properly on firestick. There is not enough memory .
Secondly, post a log in the correct forum for the addon that is giving you the problems.
how to post log file
Please see: Posting Kodi Error Logs
That is possibly the most amount of "stuff" I've ever seen on one device.
I would suggest reading the Getting Started section and Fresh Start sections here. Then install whichever ADDONS you want. If you get stuck then come back and post in the correct forum for that addon.
I'm surprised that anything ever worked on that. I've never seen so many repos or ADDONS ever installed on one box.
So first try doing a fresh start and install kodi 14.2 or kodi 15.2 .
Then add fusion from here, front page has all info. Then just whatever ADDONS you want and probably...