Docker build taking some time

I have a docker file that pulls a base image, then pulls an sdk and builds out an aspnet 2.2 Core application in the sdk layer and then copies to the base as final. THis seems to take a while to copy the files over. Not sure why (20-30 min) for 98 File(s) 7,804,458 bytes in the app folder.

It seems like it might be better for me to build the app on the local build machine (since I can do that in my case) and copy that over to the /app folder on the base final image.

Does this make sense?

Am I missing some important best practice in doing this?