If the downgrader works you'll be downgrading to the exact same 1.5 There is no differences in the firmware, so if you can get it to 1.5, it'll be a normal 1.5
I have no idea if this downgrader works, so I can't speak to that... but there is only one "1.5 firmware" so if you can get it to that point, you can do whatever non-ta082 PSPs can do with 1.5