I have a PSP that has the Dark_Alex 3.10 firmware on it. I used to follow the homebrew scene religiously from pspupdates.cjb.net, but that site seems to no longer exist. The problem is I bought Rachet ...

Modded PSP handhelds can now connect to WPA2 encrypted Wi-Fi networks, thanks to a custom firmware update. PSP’s multiplayer and online functionality have long been dead since the 20-year-old console ...

So recently there have been releases of custom firware (2.71SE-B etc) and as far as I can tell it's 'safe' to upgrade from a 1.5 to it and have the same options of running unsigned code.