I've also got 15 months between mine, so a bit of a bigger gap than you but similar issues. (DD2 born last month). It's bloody hard work. The thing I've found the hardest is the fact that DD2 cries a lot and I can't run to her assistance like I did with DD1 (also was a crier). It's not true that you become hardened to the sound of a baby crying. I HATE dummies but have been using one with DD2 because of her crying.
My DD1 was only just walking when DD2 was born and although is now more confident she does still need carrying when tired, lazy, playing up etc. DD2 just gets put on the carpet until I get DD1 where I want her!
Difficult times are when I'm trying to feed DD2 (and BF'ing so it takes a while, also she's a rubbish feeder as well) and the 5 - 7pm slot when feeding, bathing and putting both to bed. CBeebies is a godsend for distracting DD1 whilst I'm feeding DD2 even though she's not really inrested in TV much yet. Will give you my routine for the 5-7 slot if you're interested - it's still not perfect but we're getting there.
Agree with the sleep routine for DD1. My DD1 sleeps like a log usually, but has had a few disturbed nights due to illness since D2 was born and it's tough.
As for DD1 being jealous or having probs with the new baby arrives, don't worry too much about it. She's probably a bit too young to be overly jealous. My eldest loves having a young baby around and constantly tries to kiss her, however there are occasional biffs on the head for no apparent reason. You just have to keep an eye out. If you've got room for a playpen anywhere (we don't and I bemoan the fact constantly) then that will help a lot.
Feel free to CAT me if you want any adice or just want to sound off. Am equally happy to chat on here tho (as understnad you have to £ to CAT now).
Good luck with it all. don't worry you will be absolutely fine. Knackered, yes. But fine !