I second that. The from 40 to 2 per minute is quite the performance hit. So being a virtual machine on the same machine, it can not be CPU unless you have a 20 core machine and the virtual machine has only one core assigned.

Can you fit in a second network card? Then bridge it? The concept is explained here:

https://blogs.oracle.com/fatbloke/entry/networking_in_virtualbox1

If you can not. There might be a faster network emulation. Read about virtio-net in (at the end there are also performance tips):

https://www.virtualbox.org/manual/ch06.html