Up to 1999 I usually say for example eighteen thirty (1830), nineteen ninety-five (1995); From 2000 - 2009 I usually say two-thousand (2000), two-thousand and two (2002) Then from 2010 onwards I say twenty ten (2010), twenty thirteen (2013) (but here saying two-thousand and ten (2010) or two-thousand and thirteen (2013) works as well and is also used - just a bit less regularly (where I am anyway)) Difference between American English and British English is mostly the accent and some slang that is used :)

All are correct ways to say the date of course, but the common usage is to generally far the quickest method of speaking, so 2015 is frequently spoken as 'twenty fifteen' simply because it is quicker to say it like this than to say 'two thousand and fifteen'. Both are correct though. In my experience American English is generally a more sloppy and lazy way of speaking English. They frequently drop their t's when speaking for example, and the word 'gonna' for 'going to' is an acceptable word for American English but definitely incorrect.