Seems a lot of people have been buzzing about some new "downgraders" which apparently allow 2.01+ users to downgrade back down to 1.5. Please remember that the only and I mean the only working downgrade is for v2.0 PSP's. Anyone claiming to have a downgrader for v2.01 or above is just trying to either rip you off or trying to brick your PSP. Occasionally an advert for a fake downgrader will appear in the google ads within different PSP webpages.
I should add that a legit test downgrader is currently under development by PSP coder Dark Alex, but in its current stage it will almost guarantee that your PSP is bricked so I suggest staying away from it for now.
Remember that some PSP sites are posting the 2.5/2.6 Downgrader but it has bricked a lot of PSPs so until you read it here do not try it, remember safety first