In this newer version 4.15, the Post Processing Volume Settings the Blendable setting and other functions are missing

In version 4.15 some of the Post Processing Volume Settings have been moved, the Blendables Array that you were looking for was moved to the Rendering Features on the Post Processing Volume. It’s called Post Processing Materials now. Sorry you didn’t get an answer sooner, I only stumbled across your question earlier today after running into the same issue!