15 Mbps is not enough
Directv fits 6 MPEG4 HD channels in a transponder that provides 39.6 Mbps using statistical multiplexing. So the average bandwidth is 6.5 Mbps, with the better quality channels getting around 10 Mbps.
That's for 720p (60 fps) and 1080i (30 fps) Since 4K has 9x the pixels of 720p and 4x the pixels of 1080i. So with HEVC reportedly getting 30-50% better compression than MPEG4 (we'll use 50% since the math is easier) you're looking at 45 Mbps for 4Kp60 and 20 Mbps for 4Kp24.
That's just for "good quality" HD as far as Directv is concerned, which is not bad compared to the other cable/satellite providers but far from what you get with a Blu Ray. Isn't the whole point of 4K to have better quality than HD, not just more pixels but the same compression artifacting? So we really need more than those figures. 4K Blu Ray will support in excess of 100 Mbps for 4Kp24...what does that tell you?
Anyone tells you you're going to get 4K with only 15 Mbps, don't get excited. A current (HD) Blu Ray will deliver far better quality than that bit starved 4K stream will.