I have a new Sophos XG115 without any firewall rule besides the default one, with a basic license, default webfilters and no IPS activated. It is connected to a router and to a internal switch. Both interfaces have 1000 Mbps - Full Duplex Auto-negotiated. When I make a speed test I'm at around 30 Mbps Up and Down. But when I try to open a website, it takes 15 seconds or more. Before we set up the firewall it was much faster. Also over the old WLAN, who is not behind the firewall it is much faster as well.
Any idea what could cause that?
I also had this issue as I moved from UTM to XG.
My problem/solution was that I had my WAN NIC set to auto negotiate and it auto-negotiated 100 Mbit halfduplex while I was paying for a 150 Mbit line.
I changed my interface to 1000Mbit fullduplex manually and now everything works as expected.