The Dish leases on AMC-15 and AMC-16 are for the whole satellite, Ku band and Ka band. The input Dish provided to the FCC related to DirecTV's planned use of Ka band on the Spaceway satellite is related to the FCC developing specific rules on LIL HD from the framework provided by SHVERA legislation and nothing directly to do with Dish's own testing of Ka band with AMC-15. Dish does not want to be saddled with new rules related to LIL HD that have been influenced by DirecTV's announced plans for LIL HD that certainly have some technical risk.
In regards to Dish's Ka band testing with AMC-15, there are several reasons they may be conducting it.
1) Determining the feasibility of Ka band for live video which is something that I am not aware that DirecTV has done. If it is feasible, Dish may be able to save money by buying the 5 Ka band satellites that Voom ordered instead of Voom losing $100 - 175 million for canceling the satellite contract.
2) Determining the size of the dish that a customer would need to receive Ka band if it is feasible. Certainly the larger the size of dish needed, the less marketable it is to many consumers.
3) Generating a test report and submitting it to the FCC that demonstrates the problems with Ka band for live video thus providing a foundation for the skepticism that Dish says the FCC should have for DirecTV's LIL HD plans. Certainly Charlie would also release it publicly because I am sure Charlie would like nothing more than to "rain fade" on Rupert's Spaceway LIL HD parade and to influence both consumers and investors.