FWIW, a 5400rpm is slow by 2018 standards*..... while 20 seconds to open Spotify is definitely a bit longer than I'd expect on that drive, background processed, startup processes etc can all impact load times too (as can an old, bloated OS install) - so it's not necessarily down to the drive.,
*An SSD would dramatically increase your boot/load times, especially paired with a clean install. Looking about $60-$70 for a 250(ish)GB drive though. Your 5400rpm drive could then be utilized as secondary/bulk storage, provided it's still in good health.
When was your OS installed? What does your startup tab look like (in task manager in Windows 10)?
You could disable startup items, run virus scans.... potentially clean install your OS if it's been a while, but at the end of the day, you're dealing with a 5400rpm drive and the 'best' improvement you'll see, is going to be from replacing it with an SSD.