I'm not with Laminar Research, just a fellow simmer in the UK, but I would venture to suggest that deleting your preference file will not make any difference to frame rate, or atleast I've never heard this?
There are however a number of other things to consider:-
1. You haven't mentioned your PC/laptop specification, but X-Plane 11 is very 'system hungry', So, just to be certain there are no 'bottlenecks' in your system somewhere, I would recommend downloading a small piece of software from https://cpu.userbenchmark.com/, which will 'stress test' your PC/laptop to identify if there are any issues?
2. X-Plane 11 settings can also affect frame rate if they're not set to optimum. You may therefore also wish to look at a YouTube video from a well known simmer Q8Pilot on the subject of X-Plane settings, which is very useful. https://www.youtube.com/watch?v=fsum5o9IEzw
3. Another thing to consider is switching off the 'Threaded Optimization' setting in the graphics card NVIDIA control panel. This is basically an application that takes advantage of multiple CPU's, which your PC/laptop probably hasn't got! (Clearly only applicable if you have a dedicated NVIDIA graphics card)
Hope some of this helps?