It is possible that you are overloading the link and as previously mentioned that will cause higher latency. You can use a tool like iperf to measure throughput and window sizes to see if some tuning on endpoints could help with throughput.

Are you concerned about the latency issues or throughput? High latency is normal when the endpoints are far apart. Throughput is a function of latency and bandwidth. Adding more bandwidth won’t necessarily solve any issues if latency is still high (as is typical when the endpoints are halfway around the world from each other). Unfortunately the data path has to go around the globe rather than through it.