It's generally agreed that 6th will take a little longer than 5th edition on average to play. This is partially because of learning new things, but also from things like wound allocation and challenges. This actually shouldn't slow us down, as our units are almost always the same model, just x 20! In my first game, my turns actually took less than my opponents usually. Tyranids dont have characters in squads, except for Broodlords and tyrants (but I dont use Broodlords) and we only have a few options for different save units.
In 5th, we had a bit o a reputation as a slow playing army, but with other armies going infantry heavy, and other rules that mostly apply to other armies, I think the Bugs may be just as fast as any other army out there to play.