Sorry to hear that.
I tried FSLTL at EDDL to compare the result, but my FPS remained acceptable. I have an average Pc I7-7700 / RTX3060 ti / 32GB RAM and use Medium/High settings.
I didn’t use (have) an Api code so this injection is with the default settings.
General remark: I’ve understood that using an Api code means the traffic will follow the detailed flightplan including waypoints and additional data. Without an Api code the traffic wil just fly straight from "a to b ". Could this cause a degradation in FPS? I’m far from technical so don’t take my word on it.