My site working slowly because EC2 can not load large machine learning model

After you train your machine learning model, you can deploy it using Amazon SageMaker to get predictions in any of the following ways, depending on your use case:

• For persistent, real-time endpoints that make one prediction at a time, use SageMaker real-time hosting services. See Real-time inference.
• Workloads that have idle periods between traffic spurts and can tolerate cold starts, use Serverless Inference. See Serverless Inference.
• Requests with large payload sizes up to 1GB, long processing times, and near real-time latency requirements, use Amazon SageMaker Asynchronous Inference. See Asynchronous inference.
• To get predictions for an entire dataset, use SageMaker batch transform. See Use Batch Transform.

You can also look into Bring your own model https://docs.aws.amazon.com/sagemaker/latest/dg/deploy-model.html#deploy-model-steps-byom

Not sure on your set up but if you building a flask application and load the pickled file for the prediction then AWS Compute Optimizer provides Amazon EC2 instance recommendations to help you improve performance, save money, or both. You can use these recommendations to decide whether to move to a new instance type.

https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ec2-instance-recommendations.html