Java's productivity is high with good choice of libraries and an IDE that Intellij that offers fantastic refactoring, code generation and code-intention abilities. And Kotlin's productivity is even more higher since all the above apply along with convenience language features for succinct and functional-style coding.

So I would rate Java as fast and Kotlin as very fast in the dev productivity scale. You can really push the pedal in these two if you are working in an IDE and you can change your design iteratively on the go thanks to excellent tooling.