Version support in VPS - PHP

[nm78265]

'Been running host services since 1992 (no kidding) and Joomla sites since v1.5 was current. I currently run a cPanel VPS with several Joomla installations of various versions for many customers. From all I can tell, they all seem to be functioning, at least for the most part. Although I cannot bring to mind a specific anomoly, some minor issues I've encountered may be related to conflicts with the PHP version running on the server.

Recently, I was faced with installing a new site and chose Joomla 3.0 version. After the download, FTP transfer, and unpack, I navigated to the domain and encountered the error message noting the PHP version running was inadequate and must be upgraded to support J3.0.

I can upgrade the PHP version on the VPS, but I am concerned that there may be some reprocussions affecting the older Joomla sites, at least one of which is v1.5.

Can I get a reading on the damage, disfunction, or otherwise distruction to the older sites that could result from upgrading the PHP?

[Per Yngve Berg]

The latest J1.5.26 runs php 5.3 Also make sure all the extension are up to date.

[nm78265]

Appreciate that, but, I'm speaking to the lowest version under which J3.0 will operate. Is this PHP5.3?

[Per Yngve Berg]

Yes, it's 5.3