first of take your original 32mb sony memstick format it and error check it,
next download the NEW tiff-eloader 0.98 and extract to memstick as specified in readme next download the 2.01 downgrader and extract the 2.01downgrade folder to the memstick under PSP\GAME,
next goto Pictures and open the eloader folder and you psp will load the tiff-eloader 0.98,
now select the 2.01 downgrader (only item)
once selected it'll load then select the option downgrade to 1.5,
once the program has finished go back to the xmb and check your system settings for your version number (should be 1.0(note it is still 2.01 just the version is faked to 1.0)),
Now download the 1.5 eboot usa or jap doesn't matter but id recommend usa as i've never tried the jap ver,
now copy the 1.5 update to memstick-> PSP\GAME\UPDATE all capitals and run from xmb,
NOTE!!!! when "updating" to 1.5 Always make sure you have at least 70%+ battery power ideal full and the power adapter plugged in (MUST) and i'd also recommend placing it on a solid table to stop movement and kick any animals out

once complete you'll get error ffffffffff hold off till power off then turn on and re-enter first start-up set-up, setting name time timezone and language then you will have a 1.5 PSP enjoy
On a further note once you have your 1.5 use sxt version changer to fake the version to 7.50 to prevent accidental updating
p.s. as this downgrading method is identical to the 2.0 method and it is clean installing then you do not require reistalling 1.5 via 2.0 mph downgrading method.