JIRA always down, show proxy error before & after changing virtual machines (from Hyper V to VMware)

[Anere Goodness]

I have been having issue with JIRA (500 user license) & msql, server related, running on CentOS and Hyper V virtual machine together with 4 cpus & 4gb ram. As my number of users grew up to 310 and more users, the JIRA application always heard proxy error problems, availability issues  and loading issues. I did some reading and moved it to VMWare virtual machine with more cpus and 8gb ram, and ran the application and DB in separate virtual machines. 

After the JIRA was moved to a new virtual machine VMware, it became worse. always proxy error, instead of improve. My current JIRA version is 6.3.15. Mostly when this happen in the previous environment and new environment we troubleshoot, look at the logs and most of the time, we do not find any problem. How we fix the issue is by restarting the server and everything gets back to normal. 

1. I want to be certain if it is a load problem. I want to do load test. Currently i have 310 active users. Is there any scripts i can use to auto create new accounts and make them active by batch, is there also any scripts I can use to deactivate users by batch?
2. This server issues is becoming increasingly frustrating and I need the JIRA to be stable, currently its not and is very unpredictable as it affects my company process and business. Please I need advise and help on how to make it stable

[RVal]

Did you try to increase JVM Memory settings in setenv.sh ? Default settings are small

JVM_MINIMUM_MEMORY="384m"
JVM_MAXIMUM_MEMORY="768m"

May be try bumping them up to "1024m", "4096m"