There are several components at play here, apart from the vpnc package there's vpnc-scripts as well as network-manager-vpnc{-gnome}. None of these changed between 15.04 and 15.10. What did change is network- manager itself (from 0.9.10.0-4ubuntu15.1 to 1.0.4-0ubuntu5) and I suspect the network-manager-vpnc package lacks adaptation to handle your case properl. Hence I'm reassigning this bug.
** Package changed: vpnc (Ubuntu) => network-manager-vpnc (Ubuntu) -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1513437 Title: Incorrect default routing after vpnc completes To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/network-manager-vpnc/+bug/1513437/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs