It means electric motor have to produce 3045 Joule energy in 15 minutes?

No, it means 3045 Joules of energy are required to get the train up to 0.349056 m/s , no matter how long that takes.

Now how to convert 3045 Joule into watt? What's formula of Power?

In your last post you said 10 watt, how you calculated, please give me formula?

According to your specification the 3045 Joules must be delivered in five minutes, (not 15 minutes), i.e. 300 seconds.

3045 Joules in 300 seconds is 10.15 joules per second, which is 10.15 Watts.

Is this correct? A 50,000 kg heavy train is keep rotating by ~~ 3.38 ~~ 10.15 watt electric motor? I think there is some problem?

As I mentioned previously the assumption is there is no friction in this system, in reality that would not be the case.

10.15 Watts is the minimum power necessary in an idealised friction-free universe ,

in reality it would have to be more powerful than that.

[ If there is no friction to overcome a mouse could pull a train , not very quickly though ].

Without friction once started objects just keep moving : they don't slow or stop ...

http://youtu.be/-hE5nWoOcHI?t=18s