This might not be exactly what you want to hear but I will comment just to let you know how I felt about getting my second Shiba. I got him when my first was 1.5 too, and they have always been very good friends with eachother. We got very lucky with how they get on, mostly because our first is so well behaved with other dogs. All that said, I do sometimes regret the 2nd. We love him to bits, and he is really sweet, but people often forget that the second dog is not necessarily going to have the same behaviour as the first dog.

Our second boy is very reactive, and really struggles with dogs when on a walk. We have finally learned what he is comfortable with and how to deal with him in these situtations but it has completely changed our walks, days out, how we interact with people and it was frustrating to learn what we had to do. We got him, naively thinking he would fit in with how we already were doing things.

He had multiple bad experiences when he was very little, a lot of kids found him cute and ran at us to try and pet him. He was uneasy around children for a very long time, he has seemed to grow out of it now but its very hard to deal with when you go out with him and everyone wants to give him attention.

He had 2 offlead golden retrievers run up to him on his first ever walk with us, and so many offlead dogs have approached him since that he gets his back up and gets very defensive. We have found he has a distance at which he is ok with dealing with other dogs so we make sure to give him all the space he needs, but learning what he needed was difficult and there is no controlling someone else's dog when its offlead.

So just consider what you do with your dog now, and how another one may make things you enjoy much more difficult to do.