Why is running an API on localhost so much slower than on AWS EC2 instance?

I'm a new Java developer and I've been developing a small app for tracking my runners' mileage at our school. The back end is in Java and the most intense operation for the server is getting the list of all the teammates, then finding the sum of their mileage for the last week and ranking them in order from highest to lowest. When I make a call to this endpoint while running on localhost, this took 11.5 seconds! I found with parallel streams it dropped the time to about 8.5 seconds, but I was still nervous that this was way too long. I uploaded the new JAR to the AWS EC2 instance and it takes less than a second! So my question is, why is my localhost (quad-core i7 7600k with 16 gb ram) so much slower than the AWS EC2 instance for the same operation? The EC2 instance connects to an RDS instance running MySql btw. Thanks!

I get the same issue. It's probably the round trip time, rather than processing time. My laptop is in the UK, and all my AWS services are in us-east-1.

One 'action' in application might involve several trips to AWS services, for example sending a token to Cognito, getting some data from DynamoDB, then getting some more data based on the first response etc etc. It all involves several round trips from the UK to the US. Your server is probably co-located with the services you call so much less RTT.