Happy New Year to you too, Emarebe.

You can say either of those. Or if you prefer American English, you can also say 'two thousand fifteen'.

???

Now even I'm confused.

@Michael Millard. 'Twenty hundred and fifteen'.  Really? How can this be correct, if nobody ever says this?

@Bruce. So, please tell us, sir. If we are all wrong about 1801, how do you say it?

  Technically,  all dates  using a   Zero, can be read as you indicate here.

 However,  it is often the case, in the USA, that the people read zeros  as "o" (oh).

  Thus,  in dates like 1801, 1802, 1803,  1804,  1805, and so forth, many Americans commonly read this as   Eighteen---Oh---One,      and so forth.  It is not correct of course, but sometimes,  convention  holds a more powerful sway than   correctness.

  So  you may encounter  some references such as this.  However, it would be rare to see 2005  read as    "Twenty--Oh---Five"; but it would be read as "Two--Thousand---Five".

I usually say, two thousand fifteen, without the and. The and is used with numbers for the decimal like with two dollars and fifteen cents.

Hey,

We ususally use:

2015- twenty-fifteen. 

1999- Nineteen ninety-nine.

1776- seventeen seventy-six

Hope it helps. :)