Virtual Server Confiuration enhancement

Without knowing the root cause of the problem, I can only suggest some options that help improve the overall performance of your apps :

• SSL offloading: offload the server from the burden of ssl processing
• Compression profile: offload the server from the compression processing. 
• Web acceleration (caching): helps increasing the response time, and also reduce the requests going to the backend servers
• Oneconnect: helps reducing the TCP sessions opened with the servers by reusing existing connections for multiple requests.

If this is an exposed server, you may also consider enabling the ASM module to prevent ddos attacks or malicious bots traffic.

Other things may help like manually defining the maximum connections a virtual server or a pool member can handle, but this needs more understanding of the application and servers capacity