I have already googled this, everbody tells about importing data and then then 2, 3, 5 and so on minutes chart. But nowhere its told about how to create a chart of 15 minutes for last 30 days.
I now see what you want! (The added information helps.)
Two steps to achieve what you want.
1. Set the Time frame to 15 minutes and the chart to 'All Data'.
2. Drag the mouse from the last .....
But when I tried to select an earlier point in the chart, I got an unexpected response.
Have sent the response to the programmer (Simon) for his comment/reply.
Will add more when I find out the answer.