Hi guys,
When you mesh the geometry with GMSH, you will see in the log the number of tetrahedron that is written.
SPIS-UI may effectively support 1.6 million tetrahedron, but depending on the models you use, the memory cost could increase significantly (for instance, if you model electrons as particles, it is more costly than a Boltzmann distribution).
Regarding the memory limit, there are other threads discussing it in this forum. If I remember correctly, Windows does not support that one process uses more than 2 Gb of RAM. Generally speaking, we strongly advice to use Mac or Linux operating systems. That deal much better with memory.
Regards
Benoît