Yeah, they made the SoC run cooler and at lower power, so I wonder why they didn't just let it push to 20W instead of keeping it at a max TDP of 15W.
Maybe their custom APU just can't yield any more performance at all and just flattens out above that? I know the 6800U and 7800U handhelds tend to flatten out above 25-30W. I've moved on from my Deck to a Windows handheld, but I still really like the tweaks they've made to this.