after reading your comments and answers, I think that so much things are horrible to you!!
The 15Mb is the ADSL service speed that is receive by the modem wifi (router). In Argentina is a very good speed of connection. I don´t know how fast is your service, even that it´s doesn´t matter to me.
If you don´t know haw to solve the problem, please don´t miss my time.....
Read all the millions of discussions about this Apple Tv´s problem. It´s not only mine. Is a real problem that Apple don´t fix yet.
I'm in the US and ours is 50 Mbps and I ran into this issue last night for the first time ever. When it's having a problem shut it down and you can perform a reset on it which can be found here:
Mainly what I would do is if the entire show/movie is freezing up on you start loading it and pause it to give it a good buffering period, cook dinner or get snacks ready, and then come back and play it. Beyond that you just have to wait for Apple servers to not be overwhelmed and lagging which is what I'm guessing is actually causing the problems with the new addition of "iTunes Radio" on the servers (assuming the iTunes Radio working on the same servers as iTunes itself which I'm betting it is since all the music streams out of the entire iTunes stock)