using System;

using System.Collections.Generic;

​

public class Program

{

    public static void Main()

    {

        const string patternIsoFormat = "^[0-9]{4}-[0-9]{2}-[0-9]{2}T{0,1}[0-9]{2}:[0-9]{2}[:0-9]{0,3}Z$";

        List<string> dates = new List<string>

        {"2015-09-15T14:30Z","201-09-15 14:30","2015/09/15T14:30Z", "2015-09-15T14:30:13Z" };

        foreach(string date in dates)

        {

            // Console.WriteLine(date);

            if(System.Text.RegularExpressions.Regex.IsMatch(date, patternIsoFormat) )

                Console.WriteLine("Match {0}", date);

        }

    }

}