If you just can't wait a few more weeks to test out the look and feel of the new Samsung Galaxy S6 no worries developer "Albe95" has you covered. He has an app called Lollipop Theme Enabler that will allow you to achieve the look and feel of the Galaxy S6 on your Galaxy S4, S5, or Note 4. The instructions are pretty simple, but the catch is that you do have to be rooted. Once you have the enabler installed on your device you will need to unpack and load it to a certain folder. From there you will need to edit some code and then reboot your device. Head to the link below for the download and the directions.
via XDA