Hi!
There are a number of things you can look into to make the search faster. I suggest reading chapter 18 of the documentation: https://goo.gl/4OeFG1
Chapter 18.1 will offer direct tips on how to make it more performant: https://goo.gl/Rn6lG6
I noticed you are searching through custom fields as well, I highly recommend using the index table engine in this case. The post meta table can grow really fast to a huge size when using lots of plugins, and it’s not indexed. Just try a few phrases without the custom fields selected, if it’s much faster, then you should definitely consider switching to the index table.
The plugin search speed however more-less corresponds with the server performance along with the given wordpress installation – usually almost the same or less as a non-cached page load. But everything is explained within chapter 18.