The IDE versions 1.6.6 and newer are a lot slower to compile than 1.6.5 and older. More recent IDE versions have gotten a little better by caching but it's still nowhere near what it used to be. It's always shocking to me when I go back to an old IDE version to do a test or help someone and I'm sitting there waiting and waiting for the compile to finish only to realize that it finished immediately and I just didn't notice. The slowdown was accompanied with some significant improvements in function prototype generation and dependency resolution but the hope was always that the causes of the slowdown would resolved after the initial release of the new compilation system. 2.5 years later it's starting to look less likely that's going to happen.