$15/3-years is not that unreasonable for a 24-year old center. If he somehow becomes a consistent starter in the league then this is a bargain.
For comparison, Wes Johnson is a 25-year old wing who will be drawing basically the same yearly salary over the next two years should the Suns pick up his 4th year option ($10M/2-years).
At $5M a year, would you rather have an underachieving 24-year old 7-footer, or an underachieving 25-year old 6-7 wing? Why do other teams' busts always seem more likely to turn their careers around than our own? Both have been given plenty of opportunities, Lopez more, but he's younger.
So this trade is not about Wes Johnson. The Suns would be incredibly foolish to pick his 4th year option before they even see him play one game with the team, so Johnson will almost certainly be an unrestricted free agent next year, for better or worse depending on how he performs. Salary wise, he and Warrick is a wash next year. And with Warrick's expiring contract, the Suns really gain nothing and lose nothing salary cap-wise in 2013. But for this season, Johnson will provide some depth at SG/SF while the Suns logjam at PF will be reduced. Warrick wasn't going to play anyway.
But Johnson took Beasley's starting spot last year (and didn't do much with it). Makes you wonder how those two will get along. Both were probably hoping to get away from each other.
So again, this trade comes down to Lopez at $15/3-years for a lottery-protected first-round pick. Are they more likely to draft someone with more upside than Lopez with a pick no higher than #15? Or can the Suns package that pick along with other assets to get someone who can actually be part of a core? For now, this trade looks OK to me only because Lopez wasn't going to do much anyway as long as Gortat is still here. But the Suns aren't really getting back anything to get excited about either.