Size 15 dogs are going too limit your choices but if and when you find something you like -  buy a few pair.

I bring two pair of the same (discontinued) boot. They work well for me plus they are comfy. I change into the dry pair at camp when possible. In any case, I try to keep one or the other dry. Wet or cold and wet feet are not happy feet.

I take two pair for other reasons as well. One could blow out which has happened to me a few times over the years. Another is, if I'm stuck in boot sucking mud, I'll sacrifice a boot or both just to get out.