When they say a set of components, you know they mean 2 woofers and 2 tweeters right?
If aligned correctly, one set can get pretty loud. I don't know if they would "keep up" with a couple 12's or 15's, but they would do pretty well IMO.
The headroom from running 2 sets would be nice though. Are you fiberglassing your doors?
Most car audio comp sets are 4 ohms.