Memory management in any version of Poser has always been a problem. When a scene gives a problem, save it before rendering, stop Poser, start Poser again, load your scene and render (this way all memory will be available for the render and nothing will be lost for any reason). Always reduce the bucket size to force through a render (you can go down to 2 for a very slow but stable render), smaller means slower but a better chance of getting it finished.
Minimizing a program doesn't release memory, it just means memory not currently accessed is no longer in active memory, so it may give the impression of reducing memory demands but it won't actually make much difference (although several programs benefit from the small interruptions when they have some kind of garbage cleaning capabilities).
Tricky scenes will always require a trial and error method. There is no way of predicting whether a scene will be tricky, I 've had simple scenes been tricky on rendering and complex scenes (like the italian bar with 8 spotlights and 12 point lights) render without a problem, so always assume a scene will be tricky and save before rendering.