On one specific machine I've recorded the following times it takes Arduino 1.6.5 IDE to open on the following profiles:
Administrator - 3 seconds
First user - 47 seconds
Second user - 4 minutes
All the users have administrator permissions on the local machine.
Why does it take 4 mins for one of the users? Obviously, the files used are the same so I haven't replaced the rxtx*.dll file yet, but I guess that is an option as is uninstalling and comparing profiles!
Any other suggestions will be greatly received.