Yep, just take out the old and bolt in the new. No extra work necessary. Nothing to it. If you go and do it, please report your findings here after listening.
Also, keep in mind that AFAIK, all Klipsch woofers are made by Eminence, so it's not as radical as changing to other brands.
Is the Kappa 15C compatible with a B&K A/4500 crossover?