Drop in FPS with scenery

Hello fellow simmers. I am having a problem with a couple of sceneries and hope you might have a cause and solution.I have Imaginesim's KSJC (San Jose Mineta) scenery and after not having flown from there for quite a while, I experience a serious drop in FPS's when at or above the airport. I did not have this issue before. I was getting 28-30 FPS, but now I get only 4-6, a real slide show.I have not changed anything with my system and this doesn't happen with any other scenerys, except that I downloaded the Chena Marina AK28 and right from the get-go, this one also displayed 4-6 FPS.Now I can take-off from a nearby airport in San Jose, like KRHV (Reid-Hillview) with normal FPS's, but on nearing KSJC, they drop. I also use Game Booster but I had normal frames at KSJC before using that addon.So my dilemma. BTW, I did ask Imaginesim about this and received no response. So can someone here provide some insight. I will surely appreciate it.Jim D.