Hi Norvik,
One thing that will gain you memory and performance is to use work sessions. Split your file up into parts that are logical for you then you can turn on them and off easier, I also found this to be the only way to speed up and use all ram but you don’t get much more speed you get more memory for geometry.
Also blocks are ok but I think they raise memory and slow down performance because of the transform matrix associated with each block at least that was the case maybe not now, low poly meshes are the best way to really speed up the process.
Ok having said all that I think you are most likely hitting the wall with Rhino and should try 3dsmax for what you are doing.
You’ll get rendering with many more options, (one important one is to use render network which allows any machine to become a render mode and help in the process) and all the entourage and 3dobjects and libraries etc. are all there and really well supported. Also your get great animation, water out of the box with no plugins, there is so much great stuff in this field for max.
Many people I know use max for architectural vis and Rhino and other programs to build but not to render larger projects.
RM