If you update away from 1.5 you will not have direct access to homebrew unless you update to one of the custom (unofficial) firmwares.
Almost all the updates in between 1.5 and 2.71 are able to load some homebrew through a program known as eloader. It is preferable to have full homebrew access from the XMB (psp's menu), and this is only currently available on firmwares 1.0, 1.5 and the 2 custom firmwares.
If you update to any firmware up to and including 2.71 (now 2.80, but i wouldn't recommend updating that high) you can get homebrew access back by downgrading to 1.5. If you update to 2.81 or higher this will not be possible (currently, perhaps in the future).
All psp games are region free (umd movies are not), sony make new games 'require' newer firmwares as a means of forcing people to update and loose homebrew access. My advice would be to keep your psp at firmware 1.5 and use a program called devhook to load/run a newer firmware from your memory stick. This allows all newer games to run, gives you access to whatever new features there are in the firmware itself, but when you turn the psp off and back on you load straight back to firmware 1.5. This is possible because the newer firmware isnt actually installed, but just loaded into memory and run.
You can download the latest version of devhook
HERE. There should be a simple installer out soon enough if the instructions are too complicated for you.
Hope that helps.