The SSL-VPN monitor will only displays remote user logins and active connections. You can use the monitor to disconnect a specific connection. The monitor will notify you when VPN users have not enabled two-factor authentication.
But, It is not possible to see a particular user's throughput via ssl vpn monitor.
You can see the Data sheet for your FortiGate Model to see the overall throughput.
The Fortinet Security Fabric brings together the concepts of convergence and consolidation to provide comprehensive cybersecurity protection for all users, devices, and applications and across all network edges.