Welcome to the forum! 
I have 16 GiB of RAM and an SATA3-connected SSD. My system boots — from the grub menu to the sddm login screen — in about 11 seconds. So yes, I’d say there’s room for improvement.
The first thing I would recommend is to get rid of plymouth. I’ve explained the procedure in this post, although that was for doing it from a chroot environment, given that the OP could not boot from their installed system.
Secondly, there’s something strange going on with your serial ports — /dev/ttyS{0,1,2,3} are serial ports — and I have no idea what that is, because I am not seeing that on my own machine. So that warrants investigating as well.
Also, you will probably be asked by other interlocutors for the specifics of your hardware, so please post the output of… 
inxi -Fxxz