You must have many read only Data if using Os Optimization Level hasn’t changed much, you could also try O3, but this should also not have a big effect.
I have to say I’m by far not an expert in MCUExpresso which you seem to use, therefore I can not give you a complete answer. However, if your external flash is connected to flexSPI1 like it is done on the evaluation-Board, you can add the second flash to your project, like this.

I’m not completely sure if the 1060 driver is working here, but this is the best option MCUExpresso offers. If this is not working, you have to write your own driver for loading your code to the flash.
This creates a bunch of new sections in the linker file which you can use:

Now I’m also stuck. I’m not aware of a way to define that a file, or folder should be placed to a special section via a GUI option.
So either you edit the linker file or you move code via __attribute__((section("name"))).
Maybe someone else has a better idea