Yudi,

A few things you could try:

1 - save your model, close SH3D, restart it, load your model and try again
(I think SH3D has some strange memory allocation problems, and with a "clean" memory you can render bigger designs)
2 - (temporarily) delete furniture that doesn't show in the photo you want to make, then make your render in a clean machine
3 - (temporarily) delete plants and trees outside the visible area, as these take up a lot of resources during rendering
4 - share your file and I'll be happy to have a look at it

Hans