Mine are 15 months apart. Needless to say, exclusive BF doesn't really work.

(I'm kidding.)
I didn't plan them so close, obviously, and the first two years were *really* hard, particularly because it is so hard to AP. Not impossible, but really, really, really wearing. It would have been easier, I think, if my son were a little older than 15 months when his sister was born and requiring so much attention..when he was such a HN little guy and required 24/7 closeness.
Another downside? The sleep thing. Neither of them are "good" sleepers and when one of them might STTN, the other one is up. We have had exactly five nights of
both of them STTN in the past few years. Five. (Counting last night, if anyone feels like celebrating with me.

)
However, they are 3.5 and not-quite 2.5 right now, and the benefits are starting to show themselves. They are becoming good playmates. I actually didn't see them for 45 minutes the other day since they were playing together in my daughter's room. I could hear them playing firefighter and putting out fires on the bed and dresser together, and they were just wonderful together. They are playing so much pretend together, and I love it. They fight, naturally, but when they play together well, they play together really well!
That is my experience, FWIW. Closer sibs, IME, is beginning to be really fun.
