I found a bechmark test here: http://www.8088.net/blog/index.php/2011/01/24/iops-comparison-solid-state-drive-ssd-15000-7200-5900-5600-rpm/?lang=en#chart

I haven't done 15k vs SSD in a database environment, but on every machine I've ever tested on, SSD and platters just aren't comparable. Simply eliminating seek-time on random (non-sequential) I/O makes them incomparable, completely ignoring all other factors.

Collateral advantages, like lower power-consumption, and collateral disadvantages (like lower repeatable-write durability, resulting in lower MTBF), probably don't matter as much in a hosted environment, since you won't be paying their electric/cooling costs, and won't pay directly for drive-replacement if part of a RAID array fails. And modern SSD MTBF on enterprise-grade hardware is pretty good. Much better than 10 years ago. So that may not even be a factor.

But in terms of I/O, it's kind of like asking "which is faster, a Schwinn or a Porche 911?" Not the same breed of vehicle.

Of course, code-refactoring is usually the right answer to slow databases. That and/or normalization. But if hardware is critical, hopefully the above link will help.