If you care about 1.5s and other measures in the same sizes, then this post is for sure of interest to you, because you can save 100MB+ of RAM and have a perfectly functional and beauty DE with LXQt!
By the way, I use Plasma on my everyday job and I can't complain of it.
It's fast, feature full and works very well. (I never seem to understand how people complain of it being slow, bloated, whatever... Mine isn't!!) The thing I love the most in it is being able to set it in whatever way I want. I never get tired of it and so far it hasn't let me down. I'm always amazed that, whatever crazy idea I think of that can speed up my work, or make me more comfortable about my DE, they have an option for it!!!
It's a kind of freedom I can't find anywhere else.
For older computers where every MB counts (plasma uses around 350-500mb), or for people who don't care about extreme customizations (that are happy with an XP/7 like DE), then LXQt is used