Oracle: terrible execution times from virtual application server
This is almost certainly a networking issue (as the execution on a different machine is way faster) so I doubt you'll be able to go much further with any Oracle tools. I've never had any needs to tweak out-of-the-box network parameters to get good performance.

What I suggest is you use a standard network benchmarking tool, e.g. iPerf. It needs to be cross-platform since you have a mixed Linux/Windows environment. Keep in mind that the issue could be due to either low bandwidth or high latency. Run the same test from the other client from which you're getting good SQL Plus results, compare and if it's massively different send the evidence to your networking admin guys.

By the way, if you still need more advice I suggest you post to https://serverfault.com/ as you'll likely to reach more experienced network admins there.