But as author is also talking about the environment and I know it will improve but if you in to this and you have large codebase than waiting 10 minutes (some times it take 20 minutes thanks to Xcode 8.2) for build compilation and with every new Xcode release and swift release things are getting change so fast that most of time it is very hard for production app quality. Also not all dependencies keeping up at that rate.
That said I really love the language but it's my opinion by looking other languages swift is not for server development and will not be successful. But that's my opinion.
How large is the codebase? I think this is usually due to type inference on dictionaries in some cases. Usually explicitly specifying the type fixes the build times.
There's a tool that will tell you how long each part of your program is taking to compile so you can find the source.
That said I really love the language but it's my opinion by looking other languages swift is not for server development and will not be successful. But that's my opinion.