Etrechecked report attached iMac 2015 os11.6.7 SO SLOW!!!

Before you do ANYTHING backup, your internal HD is failing. Personally as the machine is now classified as obsolete rather than investing money into it (it is a base model iMac) I would strongly recommend replacing the computer.

However, it's yours and if you want to invest in fixing it then get an external SSD, clone the internal HD to the SSD and then set the SSD as your boot drive. The SSD's I recommend are:

OWC Mercury On The Go Pro & OWC On the Pro Go Power Adapter

OR you can get:

OWC 1.0TB Mercury Extreme Pro 6G SSD and a SATA to USB adapter

The least expensive is to buy an Apple refurbished Mac directly from Apple. There is no downside, identical to new, same 1 year warranty, eligible for AppleCare and can save hundreds of dollars. Get one with at 16GB RAM, 1TB SSD. Or a new Mac mini and use an external display and your old keyboard and mouse. For about $1400 you have a brand new Mac that will far outperform your current machine.

The M1 iMac would be much better and faster than the Intel iMac.

It's got the 16GB of RAM and a 1TB drive that rkaufmann87 recommended. The Silicon Mac is the wave of the future.

Without a doubt the model with the M1 chip!!!!!!!!!!!!!

Please follow the directions in Setup Assistant and Migration Assistant and it will be smooth as silk!

Nice machine.