Let's compile a list of what the different Essence Runes give at each specific level, much like TheTitan has done.
I'm assuming that if the level 1 rune gives 15 then level 2 will have 30, 3 45 etc, but let's see how it goes.
Here are the collected runes, in picture format:
courtesy of Elkilleuse in this post.
Here's a table of the required level, AP and materials for each essence rune level.