Right now the lower limit of the Dead-Peer-Detection timeout is 10 seconds. This could be lowered down to 2 for faster reaction of DPD.
vyatta-cfg-vpn: /opt/vyatta/share/vyatta-cfg/templates/vpn/ipsec/ike-group/node.tag/dead-peer-detection/timeout/node.def
I manually changed this for testing and the tunnels are up and running.