Very poor performance in navigation and speed test - USG40W

Good night,

I am configuring a usg40w for a client and I am faced with the problem of navigation speed and speed tests.

The client in particular has contracted 300 megabytes of symmetric fiber and when we connect the firewall the speed tests do not reach even 100 megabytes, they remain in about 80-90. If we remove the UTM protection layer we reach 150 megabytes but still it is half of the connection they have contracted and of course they complain about the speed of internet access.

This is normal?.

The router is doing the router functions and we have the zyxel with its ip configured in the router's DMZ.