I agree that 15 is a bit too much to field them in... Try 8 including charcter if you really want one (6 across and two to absorb wounds) with full command and the war banner, will be much cheaper than a unit of 15 and will do exactly the same job minus the numbers. But really, against most units, once you kill a few you are going to outnumber anyway.
My list unfortunately doesn't include a unit, but that is only because I couldn't afford the points to fit them in. If they had better models, I am sure they would be in there, models are important to me as well as army effectiveness. They are very cool, and while they are expensive remember they do get 2 attacks each, only drop to s4 in subsequent rounds (most cav drop to s3) and cause fear. They are right up there with dragon princes and chaos knights in terms of heavy cavalry.