Hi @Vixer! Take a look at @BenKaehler's post for details about pre-trained Silva classifier memory requirements, as well as some options you can try to reduce the memory requirements. It appears that the pre-trained Silva classifiers use a maximum of 11GB memory.
My hunch is that you'll need to either allocate more memory to your virtual machine, or run the command on a computer with more memory -- different chunk sizes and/or single-threaded mode will likely not work if you're limited to 3GB RAM. Thanks!