I think it has something to do with
RAM paging
My technical definition of the problem may be vague, but when you open the lid, the Mac loads the previous state from a sleepimage (where it was at when you closed the lid or it went to sleep). For example, if you have 16GB of RAM, it loads a 16GB sleep image upon waking it from sleep, therefore it will take several seconds, and it might take a shorter time if you have less ex. 8GB and so on.
I have tested this, and I read it somewhere on these forums too, and it seems to be in the lines with this issue. There is also a fix to remove this issue:
There should be a file called 'sleepimage', which you can remove. It will be rebuild if needed.
You should check your Power Management Settings in the Terminal via pmset
pmset -g | grep hibernatemode
The default should be "hibernatemode 3", meaning that RAM contents is written to the disk upon sleeping. To test if the reading of the sleepfile is causing your sluggish behaviour you can disable 'safe sleep' with
sudo pmset -a hibernatemode 0
I dont know if this will help for your exact problem, but it might be worth a try!
(Sorry for my English, but its not my native language)
