That's assuming this applies to everyone. Hard drive comparisons are pretty redundant these days too. An SSD will boot in under 20 seconds. A 2013 Macbook Air is around 12 seconds here:
To clear your system caches, boot up holding shift at startup (takes a long time to boot) then reboot and it will rebuild them and see if that improves your boot speed. If rebooting is something you do often, an SSD is the way to go.