I'm trying to convert this unix timestamp
in DateTime, in this way:
private static DateTime UnixTimeStampToDateTime(long unixTimeStamp)
System.DateTime dtDateTime = new DateTime(1970, 1, 1, 0, 0, 0, 0, System.DateTimeKind.Utc);
dtDateTime = dtDateTime.AddMilliseconds(unixTimeStamp);
Your code is working just fine, as is. Here is a fiddle.
Everyone that is telling you to use
AddSeconds is wrong. The number you are giving us is clearly in milliseconds. There are 31,536,000 seconds in a year. 1415115303410 divided by 31536000 is 4487. There hasn't been 4,487 years passed since 1/1/1970.