AWS VPN FROM VIETNAM TO HONGKONG

AWS VPNs do support a maximum throughput of around 1.25Gbps. https://docs.aws.amazon.com/vpn/latest/s2svpn/vpn-limits.html The actual bandwidth you do get though can depend on a lot of different factors like packet size, MTU values on your VPN tunnels, traffic mix (TCP/UDP), shaping or throttling policies on intermediate networks, internet weather, and specific application requirements. Additionally, Try to see if there is a possibility for you to use IPERF or some other tool to send more than 1Gbps continuously for around 5 mins and check if you see any improvement or not.

Also give this a read : https://aws.amazon.com/blogs/networking-and-content-delivery/aws-site-to-site-vpn-choosing-the-right-options-to-optimize-performance/