Your textures are not PBR correct, and you are lacking the most important map in the PBR workflow, a gloss map. Everything is monochromatic and really flattens out all that hard work you did with the highpoly.
I'm having some problems "downgrading" some textures from PBR to the traditional workflow, with diffuse, spec and normal. I just can't put the lighting information back into the diffuse. Should i generate an AO and put on top of it?
You should consider why you even want to move to a PBR pipeline. To be up with the times? To make things look better? Roughness/metalic shaders or AO doesnt make a game PBR. Its the LINEAR SHADING rendering pipeline. If you can't take advantage of an unclamped liner math renderer you are missing out on the entire meaning…