I know its four times as good as the full HD 1080p.Ultra HD is 2160p and super hi-vision can handle 4320p.But when i searched about them,reports were saying that it would be launched in the year 2015.Why is it releasing in 2015 and not before that,is it some kind of restriction?

No they could release it today if they wanted to. The biggest thing holding them back is price. Right now it would be extreamly expensive to manufacture and sell such a device. Right now a 70in LCD from Sony would set you back 20K dollars in the US. I am sure that could be done cheaper, but still, it gives you an idea of what a screen with 4 times the resolution would cost. With the amount of pixel on screen it would only really start making a differance around 70 inches. I don't think we will start seeing 2160p at afforadable prices until the late 20teens.

mainly because people have just started to move to current HD TV etc at the cost of several thousand dollars.

second is the fact that the bandwidth required isn't really available rite now as you might know most sources of HD content are 720p or 1080i and usually has to be compered the infrastructure for that cost millions and I don't think they would relish spending that sort of money again so soon evin 2015 sound soon to me the first sow room TVs maybe 2020 for main stream acceptance similar to what current HD technology is getting now.

And there isn't currently any physical media capable of holding a full length movie at 2160p quad layer blue ray might but blu ray is expensive now imagine how much that would cost oh holographic disks look promising but they are quite a few years off yet.

Finally evin today's high end graphics cards retailing for hundreds of dollars would struggle at that resolution to push 24-30 fps.

so you could start saving the 75k you will need for an early edition 2160p TV but I wouldn't recommend it.

what about the resolution between 1080p and 2160p

You will only benefit from those resolutions at insanely large screen sizes (250 inch and more). We are talking cinema screen size. For your average 40 - 70 inch screen size, those resolutions are "ultra" overkill.
For both home movie encoding and TV transmition, as far as 2D perspective is concerned, 1080p is as far as they will go.

As el_rika said, you wouldn't actually be able to tell the difference on a normal screen size, because of the actual limits on the human eye more than anything else.