How to network between to VirtualBox virtual machines
The problem is that the default NAT networking assigns every machine 10.0.2.15.
NAT works well for Internet access, but not to connect to other virtual machines.
Change the Network adapter to Bridged and then select an active adapter from the host on both guests.
Configure each guest with a unique address that is on the bridged network.
Bridged will allow for virtual machines to connect to each other, but not necessarily to the Internet.
Configure two interfaces: one NAT and one bridged for the best of both worlds!