I would review this section:
https://docs.fortinet.com/document/fortigate/5.6.0/cookbook/278575/limiting-bandwidth-with-traffic-shaping
however; I would definitely be very careful on throttling UDP traffic.
It sounds like there is a lot of information missing. it is hard to
guess the right solution just from little info. However below are few
links I would start with:
https://docs.fortinet.com/document/fortigate/6.2.0/cookbook/496884/overlay-controller-...
