That is not the most recent release of IntelliJ so it's at least one version behind. I should also note that IntelliJ has abandoned the version number name, the newest versions of the IntelliJ IDEs have the year now. The most recent IntelliJ IDEA is IntelliJ IDEA 2016.
That such a widely use fork of IntelliJ is behind a version is important for plugin developers who will be held back from adopting new features if they want to support Android Studio.
I think IntelliJ 15 shipped with its own JRE so it may be possible to write plugins in Java 8 instead of Java 6 for Android Studio though, so if that's true that's nice.