2017 iMac with Fusion Drive Keeps crashing every 15-20 minutes

Thanks for the Crash log however we cannot diagnose using that. I suspect the HD portion of your Fusion Drive has crashed or is getting ready to and is warning you .

Before you do ANYTHING else, backup the computer using Time Machine to safeguard your data. Do not do anything until you have done this. If you are already using Time Machine then great, just test it (try restoring any files on your Desktop) to verify it's working okay.

After you have backed up the computer then download DriveDX and run DriveDX on the HD portion of the Fusion Drive. NOT the whole Fusion Drive and NOT the SSD, only run the report on the HD!!!!!

If DriveDX finds any errors on the HD then that simply confirms my hunch that the HD is failing and must be removed from the equation.

Please report back with your DriveDX report of the HD, remember only the HD and NOT the Fusion Drive or the SSD!!!!!!!

Thanks for the EtreCheck report, PLEASE read my first post and you follow to the letter!

I see you do not backup, that is a HUGE errors and a 100% guarantee you will lose data!!!!!!!!!!!!!!!! Please carefully read Back up your Mac with Time Machine. Operating any computer without a sound backup plan is a guarantee you will lose data, data that cannot be replaced!!!!!!!!!!!! On your computer it may already be too late as I susspect the HD is already failing. You will need an external HD to backup to, I recommend the OWC Mercury Elite Pro (2 TB version is fine) and backup!!!!!!!!!!!

The EtreCheck report shows:

disk0 - ST3000DM001 4.14 GB (Mechanical - 7200 RPM)

Internal SATA 6 Gigabit Serial ATA

What drive is this, is it the old HD from the Fusion Drive. If it is that is almost for sure your problem.

There is your problem, you indicated you removed the old HD and used a SSD, you did not physically remove or disconnect the HD and that is causing the KPs.

If you are using an external SSD that is good however it needs to be setup per the directions in How to setup an external SSD as your startup disk or you will continue to have issues.