VPN takes long to go down after WAN Interace goes down

Hi, I have a branch office with a FG-30E and a main office with a FG-80E. The branch office has 2 internet conenctions, 1x DSL and 1x LTE. A wan link monitor with fail-over is configures and works fine. I also have 2 IP-Sec VPNs configured between the sites. Now here's my problem. When I set the DSL wan Interface down the failover reacts within a few seconds as configured. I can see the routing is adjustied acordingly. But the IPSec VPN that uses the DSL wan Interface still shows "up" for about 2-3 more minutes. I have a feeling that I maybe set some parameter to high within the VPN config but I cant find anything or maybe I'm too blind. When I reenable the DSL wan interaface it comes up within a few seconds and the VPN comes up shortly after.

Or is the fortigate GUI just slow? I noticed that I sometimes reacts very slowly since v.6.0.2...

Any ideas? Thanks in advance!