The .vmdk means it boots directly in VMware Workstation, ESXi, or Fusion. The .spa indicates it can handle MPLS, L2VPN, and other carrier-grade features. Together, they turn a generic server into a powerful virtual router.
IOS version 15.7(3)M3 is a mature, stable release. It offers: Vios-adventerprisek9-m.vmdk.spa.157-3.m3
Router# show license Router# show version and other carrier-grade features. Together