Polling interval for a specific volume not changing?

In NPM, I'm trying to monitor the disk utilization of a particular volume, but I would like change the statistics gathering from 30 minutes to 15.  However, when I attempt to edit that specific volume and change the Polling times, Collect statistics is currently shown at every 15 minutes however the data is only being pulled every 30 minutes still.  Also if I try to edit the specific volume and change the Poll for topology data from 30 minutes to anything else, it does not register the change.  Hopefully this makes sense  but here's some screenshots.