Here, we often experience something similar on transfers to/from the EU. The route chosen by our ISP's routers is sometimes quite slow. Connecting first to a VPN, then to the same remote server, often results in a different, faster route.

This became much more noticeable as our local connection speeds improved over the years, to the current 100/10mb/sec cable connection (faster 250/20 is available, but not willing to pay the premium for it just yet).

Cheers