im so nervous about having a 1.5 year old and a newborn
I remember I was crazy nervous when I was pregnant with my 2nd. My 1st was so much work and wore me out so much, I was so sure I couldn't handle 2 of them with any kind of grace.
And... I was right, lol. But it's worked out in the end.
It was kind of a blur, but in the end, surprisingly easy. Newborns sleep frequently, giving you plenty of opportunities to see to the needs of your older child as needed and then gradually wake up and become more alert (or maybe that was just my experience from the codeine/morphine in my breastmilk, lol). That really helped me because it was almost like being eased into parenting 2.
I did have a few separation anxiety issues from my oldest right after returning, since I had been with her 24/7 since birth (more or less) and then was suddenly missing for almost a full 3 days. That was the hardest part.
One suggestion, try to think about your current routine and how easily you could fit a second child into it. For example, my husband worked nights, so bedtime routine was 100% on me. I knew my routine at the time with 2-3 books plus plenty of songs was going to be too long with a newborn, so I shut it down to 1 book, 1 fun song, and our goodnight song. This was still "too long" according to my newborn, who I would put into her swing while giving my oldest my full attention, but I decided early on that fussing for a few minutes was worth going through my oldest's entire routine.
Chances are, one or both of your kids is going to cry a lot and you won't be able to respond right away, but that doesn't mean you're failing. I spent many times with my oldest at my feet crying while I nursed the newborn, or my newborn crying while I finished up what I was doing with my oldest (dressing, etc). It was very frustrating, and I did cry a few times myself, but in time my oldest got used to it, and she began to understand that, once I finished nursing, she would get all the attention she wanted, and because she was so young (only 1), she actually adjusted quickly.
I actually also started bathing my girls together practically from day 1. I got a bath sling for my newborn and put her at the far end. My oldest quickly learned how to play with her sister in the tub with her and even helped was her with the washrag on occasion.
I second all of what pp said. In lots of ways, its going to be easier for you to have them so close together. My kids are 19 months apart, and yes its difficult to have two little ones, but eventually they got on a similar nap schedule (dd had a short morning nap, then they both took a long afternoon nap at the same time. awesome!). Having them both in diapers at the same time wasn't that big of a deal, and they were interested in the same age group of toys/activities/etc. And don't forget the HUGE blessing it will be for them to be able to play together as they get older. My kids spend so much time playing imaginary games together or building forts together.... Honestly, you are already doing the Mama-to-little-one thing, so you might as well toss another little one into the mix
My kids will be 6 and 8 when our baby is born, and its going to be so hard to keep up with them and all their big kid activities while changing diapers, making sure we are home in the afternoons for naps.
You will do great! My DD and DS are 20 months apart and it really wasn't as difficult as I thought it would be- quite honestly, things didnt seem to get tough for me until DD was about 4 months and was mobile. The newborn phase wasn't bad and once she got mobile it was just a matter of time before DS realized that they could "play together". Now that DS is 2.5 and DD is 10 months they have SO much fun together and really do play together a lot.
I agree w/ pp that it takes some adjusting to realize that kids cry, they have to learn patience, etc. It's hard at first b/c you are used to being able to attend to your child when they need help- with 2 thats not always going to happen. I made a goal of keeping my DS' schedule very similar despite having a new baby so I was back into our normal routine of story time at the library, play dates, going to the zoo, etc. pretty quickly after having the baby (2 weeks pp and we were back to normal). I think that helped a lot b/c it didnt feel very different to him.