There are three ways of saying this: Twenty fifteen Two thousand and fifteen (mainly British) Two thousand fifteen (mainly US) All are correct and widely used.

A while ago this question came up and just about every said they use "twenty fifteen" for the year, but I've always said "two thousand fifteen". I asked my sister and she said she uses the latter, just like me. So it seems the majority use "twenty fifteen", whereas a minority (including at least my sister and I) use "two thousand fifteen". I don't know if this is a regional difference or just personal preference, so I'm interested in seeing the other answers to this question. When you're just talking about the number, you'd always say "two thousand (and) fifteen".

Two thousand and fifteen or Twenty fifteen

Two thousand fifteen is written and less casual, twenty fifteen is casual.

twenty fifteen = 4 syllables two thousand fifteen = 5 syllables Most people try to reduce the number of syllables when they speak, hence 'twenty fifteen'. All the contractions, such as: can't / don't / etc. reduce the number of spoken syllables.