So lets recap the Crackdown 2 rumors first, then we'll get to the Crackdown 1.5 ones - ok?
It started back on August 8th, 2008 when original Crackdown developer, Realtime Worlds, stated that a sequel was most definitely a possiblity. Months later Microsoft Game Studios boss, Phil Spencer, added fuel to the fire on a Major Nelson podcast; Microsoft still retains the Crackdown rights. A mere days later Ruffian Studios began to form from ex members of the Crackdown team, and rumors were already in play that they were working on Crackdown 2.
This didn't make Realtime Worlds very happy, so they released a statement. In it they denied anyone else would be working on the game because "Microsoft wouldn't want to harm their relationship with them (Realtime Worlds)."
Finally a few weeks ago Ruffian Studios officially came out of their shell and announced that game production was already underway for...something.
And now for Crackdown 1.5. What is it? We aren't quite sure but according to VG247.com the game is in development for a late 2009 or early 2010 release and will take place in the original Crackdown city but with a renewed focus on multiplayer. I have a feeling this isn't the last we've heard of Crackdown sequel rumors.