Debian 8 reached end of life over a year ago. You cannot safely use it on a production server, and we can’t support it (Webmin/Virtualmin will continue to work until it doesn’t, but we don’t make any promises about keeping it working in any future update to either. We don’t test on EOL operating systems, and won’t make any effort to fix issues running on EOL operating systems).
Your PHP and database versions are determined by and provided by your OS (and sometimes third party repos, but we try pretty hard to only use system provided packages), and you’re better off asking your package manager what versions you have installed than asking us. Webmin has a Software Packages module that you can ask about installed package versions, and most of the version info you’re asking about appears in the dashboard in Virtualmin…so…maybe just login to Virtualmin and look (assuming you’re using some Virtualmin version released in the last couple of years).