Painfully slow iMac (Retina 5K, 27-inch, Late 2015)

Welcome!

No Time Machine backup - Time Machine backup not found.

It is recommended to use Time Machine, the built-in backup feature of your Mac, to automatically back up your personal data, including apps, music, photos, email, and documents. Having a backup allows you to recover files that you later delete or can't access.

To start your first Time Machine backup, connect an external storage device. If you need one, I recommend the Crucial X8 Portable SSD - Crucial.

To learn more on using Time Machine, see Back up your Mac with Time Machine - Apple Support.

Additionally, you can use iCloud, which can automatically store your photos, calendars, contacts, notes, passwords, and more. And it includes iCloud Drive, which can store documents, desktop files, and other files of your choosing. To access those files, you just need to be signed in to iCloud. 

To learn more on using iCloud, see:

• Upgrade to iCloud+ - Apple Support
• Set up iCloud Drive - Apple Support
• Add your Desktop and Documents files to iCloud Drive - Apple Support
• Set up and use iCloud Photos - Apple Support

Drives:

disk0 - APPLE SSD AP0032H 24.00 GB (Solid State - TRIM: Yes)

disk1 - APPLE HDD ST1000DM003 1.00 TB (Mechanical - 7200 RPM)

Your Mac has a Fusion Drive for its internal storage. Fusion Drives are fairly capable, however, for more advanced tasks, and for users who want the maximum performance from their Mac, you can use an external SSD as your startup disk to run macOS and all your data from that. It will make your Mac faster for storage, and in turn, make your entire Mac system faster. For more info, instructions, and what external SSD to buy, please see: How to Setup and Use an External SSD as your Startup Disk on a Desktop Mac - Apple Community.

Jack

I have this same computer, although I'm running Catalina. A year ago I had the hard rive removed from it as it was failing (suddenly I had very little space on the drive although it wasn't full), and a new hardrive installed. Since then it's been performing pretty well, but I plan to upgrade to a Mac Studio within the year. 7 years is about as much as one can hope for with a computer these days! Hope you can solve or replace.