I'm using linux mint on virtual from past one year....its working fine no slow issue and haven't run any defrag tool
There could be any reason of a slow laptop....
1. The main reason of a slow laptop is Ram....if you have less ram then upgrade ram and if you use linux enable
swap memory (atleast twice size of your ram)
2. check start up application and disable unnecessary startup apps
3. clean junk files
4. Defrag hdd (you can try if you want it can help)
5. If your laptop is old use lighter version of ubuntu:
lubuntu | lightweight, fast, easier