MacOS will try to use as much memory as it can. Having more RAM will improve performance, but using most of what you have is not in itself a bad thing. MacOS will make room, if it needs to.
This Apple support document tells you what the various attributes mean:
Wired Memory: Memory that can’t be compressed or paged out to your
startup drive, so it must ...
Judging from the stats you provide, it seems like it may be a CPU-related issue. Try to investigate this further to understand better if the issue is RAM or CPU related.
To determine CPU use, go to Activity Monitor and press cmd+2 to get the CPU usage graph. See if one CPU is peaking during these operations or if it is multiple CPUs.
According to ...
Your model, like most Macs, supports memory interleaving, which means that paired memory may work better than single modules.
However, Apple's own guidelines for installing memory in iMacs make no mention of this, and the real-world effect may be minimal, (as mentioned in comments)