Kotlin leaves Java behind if saying about compilation speed. (You can read more here: https://medium.com/keepsafe-engineering/kotlin-vs-java-compilation-speed-e6c174b39b5d ). And recently developer team of Android announced on Google i/o 2017 official support for Kotlin language.
I have a friend, who is android developer. He sais that Kotlin is an easy language to learn, easier than Java. Kotlin has a full compatibility with Java and sometimes it's called as a next step of Java evolution