Quote from alanack:
1) Why would this setting change the amount of cpu usage?
2) Might it still not indicate that there might be some sort of hardware problem?
I'm no techie but I'd guess that with the change, you are optimizing your RAM & CPU for your system cache which your charting program uses to store the incoming live data for drawing charts.
I think your hardware is fine. 15% CPU usage is about what I get with the same machine running QuoteTracker, with spikes to 40-50% during high volume periods. It just purrs along beautifully although the 2Gig machine is more than 4 years old.