iMac Performance issue

Nothing on the report indicates any issues however your Orginal post is a little vague and you don't state what the problem is. Please remember it is a Fusion Drive based systems so it will not be as fast as an SSD based computer. Also, the HD is nearing 4 years old and it is possible it could be having issues. You can restart in the Recovery Partition (Restart while holding down Command + R) and run First Aide (in Disk Utilities) 3-4 times, if any errors appear that indicates the HD is failing and needs to be replaced. If that is the case then I'd recommend replacing it with an SSD instead.

Please continue holding down the Command key + R key until it restarts in the Recovery Partition.

Booting in the Recovery Partition will do nothing on it's own, however there are utilities in it that you can use such as First Aid, re-installing Mac OS, etc... If anything in First Aid shows up it will tell you the problem but you must understand how to read the report. What you are looking for is any errors in the Firs Aid report (remember to run it several times back to back to give it ample opportunity) If any errors appear that means the drive is beginning to fail and needs to be replaced.

Now, all of that being said, First Aid is all you have but it's not the best tool to test a drive. If you need further diagnostics then taking it to your local Apple Authorized Service Provider to be diagnosed is the best option as they have the right tools.