Yay great news!
Amy when I shifted things later I pushed both nap & BT at the same time. Otherwise all you are doing is shortening the A time to BT if you keep BT the same IYSWIM? I also started off at 15mins every 3 days, but found it was too quick for O so I slowed it down & pushed 15mins later/week.
I agree with Sara, I would also would wait another few days yet before starting to move things, as it is likely to make her OT.
xx