There is 18 months between my dc. And I'm not going to lie, in the early days I really thought I'd fucked everything up. I remember sat up cluster feeding one night, googling if I could surrender my newborn and keep my eldest.
But we found our rhythm, we had other difficulties as my first born is disabled with development delay, so for a long time it was like having twins...just one a lot bigger. We also moved house/counties when dc2 was 8 weeks old, so I do feel I was glutten for punishment 🤣
But the reality of it all was actually easier, I managed to get the dc onto the same nap schedule quite early on and I'd sleep with them too. We had no school runs or early mornings to contend with, so if we had a bad night or one was ill we could just chill in the house/bed. The dc are close enough that their development interests are shared, their games, TV programmes, activities, play apparatus, bedtimes...all the same. There is no splitting off for me and dh to give them age appropriate time, they enjoy the same things. They are 5 and 6 now and I honestly wouldn't have done it any different. They are each others best friend, they share a room, play together, amd although both have different interests still find a lot of common ground within them.
It also helps with hand me down clothing, as soon as they are boxed up they are opened again for the youngest, so no years of holding items.
The other good side is you'll blast through the boob/bottle, nappy, buggy, taking a bag to fit the kitchen sink stage quite quickly and in one go. You'll also go through the teething, night waking, poor sleep, early illnesses and all that within a short period of time without school commitments. Always a blessing!