Please check the following steps it will help you to resolve the performance issue.
Code Refactoring - by using the ANTS Performance profiler) to find bottlenecks in the code that may need to be optimized.
CSS and JS minify and compression
Disable File Watcher file on CD servcer
Disable other Sitecore config as per Sitecore Guideline on CD server
Disable search indexes
Disable performance counters using Counters. Enabled as they add overhead
Disable memory monitor by removing the hook from <hooks />
Enable static HTTP content compression in IIS
Enable IIS HTTP keep-alive
IIS Expire Web Content Header
Enable IIS Dynamic Content Compression (Optional)