it is possible you are starting to take a memory hit because there are too many files outside the native SFS archives that is being read.
To solve this, download the latest UP2.01. It will contain 90% of everything already, but in SFS format, thanx to Charlie Chap from HSFX. Then add over that only the mods and planes you find are not in it already. This will relieve your game from having to read and memorise so many files though the wrapper.dll, and serve to make smaller and more manageable your MODS folder, as well as speed up your load times.
It will also ensure that you have the latest versions of those old AAA mods, some of which were made in the beginning of IL2 modding, and had some things in that we can now do better.
Then, there are some mods that are known to cause bad FPS hits, like the Tainan Packs, because of erronious LOD values.
Lastly, you can make a habit of the practice to disable some very rarely used or exotic or duplicate slots from your air ini, as you know by, adding a // to the front of the line.
The reason this works, if because the game loads by reading the air.ini, and then using that reference to find the correct classfile (he air.whatever...part), and then reads the classfile to find the related files and 3d models. If you disable the line in air ini, the game wont read the related classes and files at all.
If you , like me, work on an "older" machine (in pc terms, anything less recent than last week), and you do not want to make an upgrade, then the above solutions will serve you well.