Initializing DynamoDB Instance has a bad performance

Question

I'm developing Lambda functions with .Net Core 3.1 and trying to use high-level APIs to manipulate the DynamoDB.

   var db = new AmazonDynamoDBClient();          // this takes over 2000 ms
   var table = Table.LoadTable(db, "my-table");  // this takes over 1500 ms

It looks like a very bad performance but I don't know how to improve it. The Lambda function was deployed in the same region under the same AWS Account.