This iCal event has a single recurring rule, that allows this event to take place 15 times. The rule doesn't define the end date (Until property is null), but rather defines the number of events (Count property).
Please take a look at this unit test:
IMail mail = new MailBuilder().CreateFromEmlFile(@"c:\ends after 15 events.eml");
Event e = mail.Appointments[0].Event;
Assert.AreEqual(null, e.RecurringRules[0].Until);
Assert.AreEqual(15, e.RecurringRules[0].Count);