LOL

So because Windows started up SO quickly, I had assumed I’d installed both OS’ on my SDD.

Nope! Both were on the HDD.

Deleted my Linux partitions on the HDD, popped Debian on the SDD, KDE starts in 3 seconds.

Still very strange to me that KDE took almost 3x than Windows on the HDD though…

@james This is just a guess, but it might be because of fast startup in windows. With fast startup enabled (which I think it is by default), windows hibernates instead of shutting down.