I've got 3, with 15 months between each one.
The important thing to remember (and I'm sorry if this sounds like I'm stating the obvious!) is that 15 months is still a baby. I say this specifically because I know I forgot it time and time again. It's only when I look back now on photos of when DS1 was born, that I see how much of a baby DD still was herself.
So the number one piece of advice is not to over-estimate what your DD should / will be able to do. In some ways, I found it easier to think of them as twins, but with slightly different skill sets!
I don't have any sound advice about things like matching up their nap routines, because mine were disastrous sleepers anyway, so I just used to put them in the double buggy and go out for long walks in the hope they'd go to sleep!
I think if you're going to be sitting and feeding the new baby for any prolonged period, you need to make sure you've corralled the older baby successfully, with enough stuff to interest them, and no means of escape!
We got DD a little baby doll and accessories just before DS1 was born, so whenever I was changing him, she would trot off and get her baby too! DD absolutely loved DS1 from day 1 (I think DS1 was a bit more ambiguous about DS2 when he came along!) and she was very gentle, so I moved quickly to bathing them together, sitting them in the cot together if I needed to tidy their room or anything.
Also, I don't know what your relationship with DH / DP is like, or how you split the work at home, but it's vital that you have him completely on board and ready to do things. Actually, I would give this advice to anyone having a second child, whatever the gap. I think a lot of the stuff I found hard could have been helped if I hadn't had such a complex about doing everything myself.
Overall, I think I really avoided any of the sibling rivalry stuff that you hear about from parents with a 2 - 3 year gap. None of my DCs can remember a life without the others, and whilst we're not without our problems, sibling rivalry really isn't one of them (so far...!!)
Now (and they're 7, 6 and 5) the small age gap is completely fantastic. They're all entertained by the same days out, same films, often the same books, they all eat the same food, they're all in infant school together so they look out for each other at playtime. I really wouldn't have it any other way.