That's a shedload of power to be hitting a 1503 with. I hope you weren't using all of it.
I'd start with playing music through them, but roll off the bass so the mids and horns are doing most of the work. Bring them up to a reasonable volume. If you hear distortion, try to locate its source -- mid cone(s) or HF horn(s). If everything's good even when loud, bring up the bass and roll off the mids and highs so the fifteen is doing most of the work. Listen again for distortion.
Another thing you can try is to feed a sine wave at various frequencies to the system. Try 100 for the fifteen, 700 for the mid cone, and 4K for the horn. The frequency that distorts (again, at a reasonable volume) will tell you which driver it is. But be forewarned: it is VERY easy to burn voice coils with sine wave testing, because you're using a 100% duty cycle. Watch your volume when you test with a sine wave, and do it for only a few seconds at a time. I mean like three or four, no more than that. Compare the two sides to see whether one driver can go louder before distortion than its opposite twin.
How do you tell whether it's the crossover or a driver? If only one side is exhibiting the problem, you could swap crossovers between systems. If the problem moves to the other side after the swap, then you got lucky and your troubleshooting is done. If it's both sides, you'll have to do your sine wave testing direct to each driver, using the appropriate frequency in each case, with nothing connected to the driver except the power amp that's sending out the sine wave (i.e. disconnect the leads coming from the crossover). If things clean up with the crossover out of the picture, then you have your answer.
Also call Carvin tech support to see what they have to say. They keep thick notebooks on this sort of thing and may have a tip that will save you an hour or two of test time.
Hope this helps.
