Okay, PHP should be fine. Ubuntu 14 is EOL unless you've purchased Extended Security Maintenance, but this shouldn't affect osTicket much. Are you able to upgrade to 16 or 18? By default, this would give you a more up-to-date PHP version too.
What about MySQL version? Generally if 1.10.6 works fine then I can't imagine there'd be any other system settings that would cause issues, but maybe someone more knowledgeable than myself in this matter would have better advice ?