For some details, the slightly related yet different fps issue was fixed by a specialized ddraw.dll linked by Alberto in his stickied thread. That file picks up all of JJ2's DirectDraw calls and processes them properly and with some custom settings too! The problem was that DirectDraw, which JJ2 calls to for fullscreen mode, was officially 100% unsupported by Microsoft's new window manager in use since Windows 8 (it's WDM). As you may know, DLL files are first looked at in the same folder as the EXE so that devs may supply their own version for compatibility. Placing the special ddraw.dll in the JJ2 folder will make JJ2 use that one for DDraw calls instead of the one(s) in the Windows folders.

Though I lack enough feedback to confirm this, the fps problem apparently didn't happen for everyone and likely depends on CPU/GPU combinations.

And as I said before, people using Intel graphics adapters (including those on multi-GPU laptops that can switch between them on demand) have always been immune to the fps problem.