Appsync, Serverless Lambda, RDS (aurora postgresql) API response taking more time (avg. 1.5sec)

Hi,

Firstly, we need to find which part occupied the most long time. Have you checked the duration of Lambda?
You can check the aws lambda cloud watch log and observe the report[1].
You should see the following output:

START RequestId: 57f231fb-1730-4395-85cb-4f71bd2b87b8 Version: $LATEST
"AWS_SESSION_TOKEN": "AgoJb3JpZ2luX2VjELj...", "_X_AMZN_TRACE_ID": "Root=1-5d02e5ca-f5792818b6fe8368e5b51d50;Parent=191db58857df8395;Sampled=0"",ask/lib:/opt/lib",
END RequestId: 57f231fb-1730-4395-85cb-4f71bd2b87b8
REPORT RequestId: 57f231fb-1730-4395-85cb-4f71bd2b87b8  Duration: 79.67 ms      Billed Duration: 80 ms         Memory Size: 128 MB     Max Memory Used: 73 MB

You can check the Duration and Memory Size and Max Memory Used to determine whether to increase your lambda memory.

[1]https://docs.aws.amazon.com/lambda/latest/dg/monitoring-cloudwatchlogs.html#monitoring-cloudwatchlogs-console