$15k huh? You know what I think (not that anyone cares ). I think that if you took , let's say, 10k of that money and hired a MASTER teacher (one who is or was a seasoned 'pro') to bring you to a new level of musical proficiency (in both theory and playing technique), you would be able (using ANY arranger, not just the 'latest/greatest') to create a more satisfying musical experience than anything you could ever do merely by changing arranger keyboards. Being more 'personally' invested in your music will bring a deeper and more 'personal' kind of satisfaction. JMO, of course.

chas