Don't ever try and use the millisecond difference between two times to calculate the differences, there are just to many idiosyncrasies with date/time calculations which can cause all sorts of erroneous errors.
Instead, save yourself (alot) of time and use a dedicated library
Java 8
LocalDate start = LocalDate.of(2015, Month.JANUARY, 1);
LocalDate end = LocalDate.now();
long days = ChronoUnit.DAYS.between(start, end);
System.out.println(days);
Which outputs 69
JodaTime
DateTime startDate = new DateTime(2015, DateTimeConstants.JANUARY, 1, 0, 0);
DateTime endDate = new DateTime();
Days d = Days.daysBetween(startDate, endDate);
int days = d.getDays();
System.out.println(days);
Which outputs 69
