Iirc with time mechanical drives do slow down significantly due to wear and tear so it kinda sounds its on its way out. If speed is a must maybe look at how much storage capacity you’re using and switch to appropriate sized ssd/s. You can keep the mechanical drive as a cold backup.
Edit: not sure if you already done this and I usually don’t recommend it if you don’t have backups but benchmarking would show you the read and write speeds. Also depending on warranty status, you also have the option of doing a manufacturer replacement. Not sure what info Toshiba asks for but doesn’t hurt to look into if you do decide to replace it.