I've finally decided to start working on a Joomla 1.5 migration plan. The main thing that has been holding me back is my search engine optimized URLs from Joomla 1.0.15 which are being generated using OpenSEF. Being that OpenSEF is no longer supported, there is not a Joomla 1.5 compatible version of the plugin.
At one point, I tried to migrate from OpenSEF to sh404sef, but quickly realized that they use the same folder structure and I couldn't do a swing shift. When you try to install sh404sef, it will try to install it in the same folder that OpenSEF is installed in.
Swing Shift: OpenSEF active > Install sh404sef (inactive) > Deactivate OpenSEF and activate sh404sef > Uninstall OpenSEF
That being said, I've realized that sh404sef is Joomla 1.5 compatible, so my plan is to set up a cloned version of my current site and migrate the URLs on the clone site to use sh404sef using a simple shift then try the migration to Joomla 1.5 on the clone site. Assuming things go well, I'll then perform this on my production site.
Simple Shift: OpenSEF active > Uninstall OpenSEF > Install sh404sef