Caliburn Micro passing data with the EventAggragator and opening time of Views

Question

I read a file on disc in one ViewModel and at the end i send the data to another Viewmodel via the EventAggregator. When i switch to the View of the other Viewmodel (with ActivateItemAsync) it takes 10 seconds before the View opens ! The data consist of an ObservableCollection of some 80000 strings.In this 10 seconds the CPU usage is at 25%. What is happening in these 10 seconds ?

If i send only the filename to the other ViewModel and reread the file in the OnActivate method, the View opens in 2 seconds !

And what's the difference between Conductor<Screen> and Conductor<Screen>.Collection.OneActive ?

I got a ShellVieModel : Conductor and all other ViewModels : Screen

 public async void ReadNCfile()
    {
        LinesNC.Clear();
        await Task.Run(() =>
        {
            Regex regexline = new Regex(@"^N[0-9]+");

            int i = 1;
            foreach (var rawline in File.ReadLines(SelectedNCItem))
            {
                LineNCFile line = new LineNCFile();
                line.Index = i;
                line.NCLine = rawline;

                Match match = regexline.Match(rawline);
                if (match.Success)
                {
                    int number;
                    bool success = (Int32.TryParse((match.Value).Substring(1), out number));
                    if (success) line.LineNumber = number;

                }

                Application.Current.Dispatcher.Invoke(() =>
                {
                    LinesNC.Add(line);
                });
                i++;
            }
        });

        _eventAggregator.PublishOnUIThreadAsync(new NCFileChosenEvent(LinesNC));
    }