As Nick alluded to, make sure you have updated 5.2 with the hotfix. Shift Z works fine for me.
My last bit of advice is untick Vector, if you have it installed. That was the difference for me of a flat Philippines and then bang, the place came alive with 3D houses, palm trees etc. the way it was meant to look.
Give it a try, nothing to lose as you can just tick the box again to get it back.