No way,
From my personal experience on my machine with 6gb ddr3, 5400rpm disk, i5 3rd gen KDE is so annoying to use and even multitasking is laggy while on xfce it's very smooth relatively.
This was observed on Ubuntu, Arch and opensuse. Opensuse KDE was the worst of them all while arch with Xfce ran the fastest of them all.
Sounds like a configuration issue somewhere. I've run KDE on several computers with no lags, and I am quite sensitive to lags.
I also run KDE on an under-powered (even at the time it was released) x86 tablet released in 2011 (the Airis Kira Slimpad - Intel Atom N450 1,66 GHz, 1 GB RAM DDR2 @ 800Mhz, Intel GMA 500). It was the only desktop environment that was kinda usable on a tablet at the time. It's slow (this tablet is exclusively used to play music by auto starting Clementine), but not slower than anything else.
A 5400rpm disk is tough though with today's distributions and maybe Xfce does fewer disc accesses than KDE. You probably should disable desktop search if you haven't.
I guess it's the hdd thats causing the problems. I guess your tablet has emmc flash storage causing it to be pretty responsive compared to my machine that's better spec and newer too........
I think your issue is the 5400rpm disk. KDE uses a lot more of dynamic libraries (for various plugins) compared to xfce. On hard drives, that means a lot of random disk accesses, which tends to slow down startup speeds a lot.
