MySQL performance slows down when accessed from different regions via the Internet
If you have a lot of back-and-forth between your front-end and your database,  network link latency could kill your application's performance.

Measure ping times between your US front-end and your Brazilian database server. Your front-end needs to wait for that round-trip time for each and every database access (sometimes more than once per request).

If this is indeed your problem, then I'm afraid there is no easy fix for latency generally speaking (unless you can find a provider that has a more direct route to your Brazilian endpoint). Adding more "bandwidth" (Mb/s) won't solve high latency issues.
You need to keep your front-end closer to your database, or reduce the number of database calls.