A lot of things could contribute to it taking longer.
- Age of computer and more specifically the hard drive
- Dust and dirt build up on the CPU / and heat sink can cause the CPU to throttle down
- If it's a spinning disk hard drive the fuller the drive is can cause additional seek latency to find and remove data
- Potential malware running on the system
- Corruption in the operating system
If this computer hasn't had a fresh install of Windows in a long time, I'd suggest backing up data and re-install Windows. That should eliminate several of the potential reasons for the slow down.