One of the most common pains for users of AWS Lambda is cold starts. Cold starts add unwanted delays to Lambda invocations, and in cases where a Lambda is used inside of a Virtual Private Cloud (VPC), the latency can be as high as several seconds. This practically negates the speed benefits of Lambda functions.

Fortunately, the Lambda team announced at AWS re:Invent 2018 that they are changing the architecture of Lambdas running in a VPC in order to reduce this latency and make Lambdas start much faster.

https://www.nuweba.com/AWS-Lambda-in-a-VPC-will-soon-be-faster