Hi,

Have draytek 2820Vn's for branches and head office.

CRM and File Server is in HQ and all the branches connect to the HQ server for CRM and file serving.

User's finding it slow - this is due to the bandwidth being used up in HQ
can the 2820Vn have QoS for each of the VPN site-2-site IPSEC tunnels so I can restrict each branch vpn tunnel to not use all the internet bandwidth ?

You should be able to, yeah.
You'd need to make a Class in the QoS section with the source / destination IPs of the remote network then in the Setup section for the WAN connection you're using, you can then reserve a percentage of bandwidth for each class, beware also that Class 1 should get higher priority than Class 2 & 3 as far as I know so it may have lower latency.

Another way, under bandwidth management, I'm not sure if it works in this way but enter the IP addresses of the remote VPN and specify the amount available to use for each IP range.