If you mean "through" floors, I can't say for sure. It is only a small level RF signal. My guess would be no. If you really mean "across" as in on the same floor, same room, yes. 15 foot should be withing its range.
No, but I had the less expensive MK270 for an HTPC in my living room for awhile. It has a 10 meter range and worked beautifully for me at about your distance. Sorry, I can't say for sure about thru floors. I was thinking you mis spoke and meant across floors. I'm presuming you must have your PC on one floor and your TV on another. You could test it with the TV's remote thru the floor. It works off the same RF type signal.