F/w 1.5 is like basecamp #1 for homebrew.
From there you can upgrade to a custom f/w, that enables your PSP for homebrew and official software.
All CFWs allow a return to 1.5 (and from there back to 2.6 if you want)
A common route from 2.6 is:
upgrade to 2.80
downgrade to 1.5
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