Hi,
I will skip the lecture since I guess you know 1.5 is end of life and 5.4 php is close. There is a process to go through, painfully to drag your version of Joomla up to running on php 5.4. Ideally php 5.5. If you are certain this is the route you want, rather than an upgrade to Joomla 3.0 etc, then I will get it done. It will require testing and input from you once done since the conversion from 5.3 to 5.4 involved various tiny tweaks on a few php functions (pack, case sensitive variables in some contexts) and a couple of others. Can you make sure I have the Joomla login and db passwords as well as the digital ocean and remote passwords please. Note that [login to view URL] flat out state that 1.5 DOES NOT run on PHP 5.4
How big is your 1.5 website (web pages/users/DB size)
What version of 1.5 are you running - the first stage is to get to 1.5.26 ideally, but that depends on what you have had as special mods are done to yr Joomla if it is not on 1.5.26? As the upgrade to 1.5.26 might not be site friendly for your site. Do you have a working (on-line version) of your site somewhere? Otherwise it might be best to start from ubuntu 12 which supports php 5.3 -- at least then there is a working reference point.
Do you have a long term plan for this site (as it is so far behind security patches that you would not really want to let it near the live internet).
Best regards
Mark