One video of the scenes in question for others playing along at homehttps://www.youtube.com/watch?v=GTwNXWoqQlo
Randomly changing things with a hex editor is not going to work. That might find the data you want as far things like graphics, levels and music as it will become corrupted in the game but this will require a tiny bit more finesse. Likewise "editing speed" is not a unified concept so you will probably not find much grouped under that heading -- text, game control speed, PAL<->NTSC, animation speeds, music speed and button reaction speed can all differer pretty radically from game to game, never mind from concept to concept. About the only similarity is on older consoles much of it is tied to the clock speed of the device (why so many PAL ports are less than stellar) than some more time aware concept like in newer systems and modern PCs.
Here it appears to be fairly normal animation, and probably text at that, with characters coming in mostly one by one (not sure about those ... sections but it is not going to be all that different) with a fair delay.
There is also animation of the "stills" up the top of the screen. This may be nothing or it might be something if they both use the same timer and you try speeding that up.
When we do this for sprite animations you can sometimes find coordinate patterns to edit (skip the middle sections and it animates faster and thus finishes faster), here the only way you are going to avoid assembly is if the game uses some kind of serious text engine that has the delay stuff built in. We have seen such things in games on many occasions but not many would place money on it happening in a megadrive cut scene.
Anyway you are going to want to find a debugger (not sure what we are suggesting for the megadrive these day) and use that to find the routine that is drawing the text. From there you will hopefully know how the engine works in this case and can either change the timer or the values that the draw routine responds to. I guess you could also force a full dump at once but that is probably going to be more effort than either of the others.
Again hopefully the text is decoupled from the animations on the top screen -- watching them many appeared to aim to be somewhat slow and ponderous and having them play at double speed would probably mess up the tone a bit.