Ok, so what it looks like is connections waiting on your searches to finish, so they pile up behind that. You really don't have that much data, so it shouldn't be taking that long to search.
The odd thing is the search has been this way since 7.0, but you said you're just starting to see issues recently.
You might have answered this before, but are you on a shared server, virtual private, dedicated? You could probably see some improvements on this if MySQL was tuned properly.
I'd also suggest turning off searches for guest users if it isn't already. We will be making some major changes to the search for 8.0 to help, but from those screenshots, your searches are taking well over 10 minutes to complete, which isn't normal at all for the amount of data that you have.