A friend of mine stated his Laptops battery life goes down to less than 2 hours (from

if he uses the CD drive. Imagine a device that constantly accesses it. But then again, that won't be the selling point of the PSP.
Sony focuses on power and features, while N prioritizes size and battery life over the rest. Nonetheless, the lifetime isn't important for most buyers (at least prior to buying) so N won't score with that.
So it depends on the games: Sony can't get GTA for the PSP, as GTA1&2 are on GBA and 3 won't run on the PSP (requires better hardware). While Nintendo currently scores with having the most popular franchises on the GBA (e.g. Pokemon). If sony can't deliver a "killer app" most people will reason that for USD200 they can get a full console and get one instead. Parents will more likely get their kids a GBA than a PSP, just because of the price.
boggy b: If the thing can handle 15mps, it can handle 15mps. Slow down would mean it had to draw more than 15mps. Millions per second is a unit that includes time, so it is irrelevant whether it's 15mps@60FPS or 15mps@30FPS. The latter just has more polies per frame.