Basically, the 1527 is a reissue of the 7620. The operative word here is "basically," as there's a few differences:
-Pickups - the 7620 comes with Dimarzio New 7's, while the 1527 comes with V7- and V8-7's. The general consensus is that both should probably be replaced, but I can tell you that my first thought when I first plugged in a 7620 was, not knowing they were spec'd with Dimarzios, "Man, Ibanez's stock pickups have really gotten a bit better in the last year or so."
-bridge. Edge Lo-Pro vs. Edge Pro. Performance-wise, these two are pretty close, provided that you swap out the regular trem studs for the lo-pro style locking studs. Huge mistake on Ibanez's part to downgrade this spec, but barring that, the trems handle basically the same, and actually my experience with the Edge Pro has been that it's got a slightly smoother feel, and the stainless saddle inserts are, to me, a great touch. Besides, it looks cooler.
neck - profile should be the same, fretwire should be the same, but you've got a one- or -three piece neck on the 7620, and a 5-piece on the 1527. I've heard arguments back and forth on which is better - a multi-laminate is less prone to shifting and flexing, but because it's made of more pieces of wood a one-piece is less likely to crack - but the upshot is my take is that a well-made one-piece and a well-made 5-piece should perform quite similarly over time. Cosmetically, I like the new 5-piece.
Price - this one's tough. at $1400 list, the 7620 was overpriced (seeing as the UV was at the time only a few hundred more), but they got cleared out for cheap and can routinely be had for $4-500 in UV1000's with aftermarket pickups these days. The 1527 was priced more intelligently (if nothing else, it had to compete with the used 7620's on the market), and goes new for around $800 these days I think. I haven't seen too many of these used yet - it seems that most people curious about trying a seven go for either a used 7620 or a Schecter these days, and the ones who buy 1527's are already hooked, and hold onto them - but it looks like second hand pricing for a good one seems to be settling down around $600, depending of course on condition and pickups.
Allow me to stick in the abligatory bit 'o whoring for http://www.sevenstring.org
where you can find a ton of players who own and have played both - we're down for a server change today, but should be back up later on in the evening.