When I select the "copy objects" option, it doesn't copy, nothing happens. What should I do to copy objects so I don't have to keep importing tracks.
There's no "copy objects" option in MM-15 (only copy, paste, etc...), but I'll try to help There may be a couple of things going on here.
Are you PASTE-ing after you copy? (You didn't say that you were.)
Are you aware it will paste the new object on the same track at the red marker? You have to place the red marker at an empty space on the same track or else it will paste the copy on top of the original object. You may have one or more copies on top of each other without knowing it.