I think Lollipop uses ART and it'll be a standard thereafter. I was able to convert to ART on my Access but not on my Prime. Didn't really notice a difference, other than it made every file quite a bit larger.
Android Runtime (ART) is an application runtime environment used by the Android operating system. ART replaces Dalvik, which is the process virtual machine originally used by Android, and performs transformation of the application's bytecode into native instructions that are later executed by the device's runtime environment.[1]
Unlike Dalvik, ART introduces the use of ahead-of-time (AOT) compilation by compiling entire applications into native machine code upon their installation. By eliminating Dalvik's interpretation and trace-based JIT compilation, ART improves the overall execution efficiency and reduces power consumption, which results in improved battery autonomy on mobile devices. At the same time, ART brings faster execution of applications, improved memory allocation and garbage collection (GC) mechanisms, new applications debugging features, and more accurate high-level profiling of applications.[1][4][5]