I have 11 months between DD2 and DD3 (they were born in the same year) and 13 months between DD3 and DS4...so 24 months between all three.
As they get older it will get easier but I do have to say it is probably a little to close...I am absolutely exhausted most days.
My DD1 and DS1 are 17 months apart and i think that is an awesome gap...they are still really close at 14 and 15 (though they have there moments.
The first few years with close children are the hardest...but it does get easier.
Make sure you have a really good double pram...it makes it so much easier to get out of the house.