Do you experience this slowness only on the first invocation of a particular plot or always. The former is expected -it even has a name “time to first plot”- the latter should not happen.
The reduction of “time to first plot” is actively being worked on (yes it was a lot worse). It is caused by Julia compiling the needed functions on the fly (precompilation only does half of all the compile work).
If you search for “time to first plot” you will find a large amount of reading material…