Migrate and optimise an old, difficult, Joomla 1.5.26 website.

General information for the website: FREE WEB DIRECTORY helping families FIND groups, programs, networks, and resources that speak or support their LANGUAGES.
Description of every page/module: This is the multilingual website: https://www.google.com/?gws_rd=ssl#q=languagetree.org

It is very out of date. Two people have failed to migrate it so far. They said the plugins no longer exist, and the content cannot be transferred.
Description of requirements/features: This is the message sent to me by the hosting service - InteractiveOnline.

[Your site is a high resource usage site and requires more processing power than a typical site. This could be due to the fact it is still using a very outdated version of Joomla 1.5.26 which reached its end-of-life cycle back in September 2012. You should have taken steps to migrate to Joomla 3 years ago. Aolso the site needs to be optimized. I see it has a Page Speed Grade of a D at http://gtmetrix.com/reports/languagetree.org/msZVJkKm .]
Extra services needed: Optimization
Extra notes: