Report showing 'time spent' above and below 15 minutes

Report showing 'time spent' above and below 15 minutes

Good Morning,
 
I would like to create a report that shows out of all requests logged (last week) how many of them were closed in under 15 minutes and how many were closed in over 15 minutes. It would be great if I could also get a bar or pie chart to represent this data.
 
Many thanks

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