4 layer stackup Eagle
Eagle doesn't have a concept of specific purposes for copper layers beyond top and bottom being used for component placement.

Your layer string is fine for what you need. (1+2*15+16) creates a four-layer board with no blind or buried vias.

You will get in Eagle the four routing layers, 1, 2, 15, and 16, which are all simply copper layers that you can use for any purpose.

If you want to use the inner layers for VCC and GND, simply draw polygons on layers 2 and 15 and name them for the appropriate net.