Link degradation after changing to XG firewall

Hi,

we recently replaced a UTM firewall with a XGS126 (SFOS 19.0.0 GA-Build317). We haven't changed anything else, the network config is the same.
On this site we have a 10Mbps WAN link and two 2Mbps MPLS links (active-passive). We are ICMP monitoring the firewall on the MPLS IP and the two MPLS routers. With the UTM the response times were always around 60ms. Since the change we regularly get response times above 400ms and even drops to a point where we cant access the webadmin over the MPLS link. For testing purposes we switched back to the old UTM for one week and everything was fine again. Is there something on the new XGS that could cause this behaviour? 

I also wanted to limit the bandwith for the MPLS links (similiar to the Traffic shaping settings under System services but this is only for WAN). For example instead of 2Mbps I want to limit it to 1.8Mbps and see if it changes anything but where can I do this on the XGS? 

We also tried to disable SNMP traffic to see if anything changes but with no effect.