2015 iMac SSD external upgrade issues

[holdski]

Hi everyone. I’m at my wits end.
I have a late 2015 iMac that’s slow as all hell and really frustrating to use.
I saw that you can boot from an external SSD and it looked pretty easy so I went out and bought a 1TB crucial X9 pro and a usb c to usb adapter as my Mac only has USB and thunderbolt ports.
I booted into online recovery mode, downloaded Monterey and installed on the SSD and set the Mac to boot from the SSD itself.
The trouble is that I don’t have to set up any options like region, password etc it just boots to desktop and it feels slower than the internal HDD and takes ages to actually boot.
I did a speed test and it comes back with a read of 40/70 MB/s and a write speed of 66.6 MB/s.
Have I done something wrong as most people seem to be getting read/write speeds of 400+
Any ideas guys and gals?

 

[Imac Sam]

It’s your adapter. Make sure you got a quality one that truly supports at least 5Gbs speed. At this point that transfer rate is USB2 speeds.

 

[holdski]

It’s your adapter. Make sure you got a quality one that truly supports at least 5Gbs speed. At this point that transfer rate is USB2 speeds.

This is the one I have and it states 5Gbs!

 

[holdski]

Could you recommend one that would be more suitable for my needs please?

 

[Fishrrman]

For the adapter, try this:

https://www.amazon.com/Amazon-Basics-Charger-480Mbps-Certified/dp/B01GGKYKQM/ref=sr_1_6?dib=eyJ2IjoiMSJ9.sZHTMgA7efLMWFpqPjBwqxG9Jdj3DM4vwdkat1v1qMS02_BgyAsvCEVL7y6q9DHT1HsMmTLML4ZipDlIimVBISyjLG32C_25knpzNTFchSP_4-Cbpf4EhYHMiUl_0sIZMm0wL6bFP0c_DoPeex7al06z8I5Q4KjTt8qHz0vVg0mL6t9wqOk_mud4vmGW635hCxYz5P2hHIE34BwcJ15rQubOYEgQq19rDOK5ljbtLbk.ocVGEIdGJuoFf0yjdUW-e1HfswvByNvvNThVQZGxorc&dib_tag=se&keywords=usb%2Bto%2Busb-c%2Bcable&qid=1726668993&sr=8-6&th=1

In other words, don't use one of those "tiny" adapters.
Use an actual -cable- with USBc on one end, and USBa on the other.
One that is rated to be a "charging" cable.

Crucial X9 pro looks to be a USB3.2 (also called USB3.1 gen2) drive.
Plugged into a USB3 port, you should be seeing reads around 420 and writes perhaps a little less.

Do you have another Mac available that you could try the drive on?
Not "to boot", just to run a speed test on it?