t3 large? I'm on t3 medium, but website slows or stops

I'm going to assume that you're hitting some CPU or some memory limit which is causing your instance to respond slowly. You should also ensure that you aren't running out of CPU credits with a t3 instance: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/burstable-credits-baseline-concepts.html

Have you considered using CloudFront? You can put a CloudFront distribution "in front" of your instance; get auto-renewed TLS certificates for free from AWS Certiciate Manager; get 1TB of free data transfer; content caching (which will help reduce the load on your server); and you could use WAF, Lambda@Edge or CloudFront Functions to block malicious traffic without consuming resources on the server to do that.