Approximately how many levels per world are there in the episode? If you only on world 5 then it must be high. And I have no idea how on earth you got it to be so big.
I think we need to know how long the soundtracks are in the game, and you really need to decrease the size by like a lot because the current size alone could make a fair few users lose all interest in an otherwise good looking episode, whether it be because they don't want to wait or use up that much storage and for some, not having good enough internet/PC to download something that large (I have doubts about this myself TBH). If you have 30 min+ extended tracks then cutting it down to just a few minutes would greatly reduce the size of the tracks. There is a reason contests had a rule that penalized music tracks over 6 minutes, which was to keep the size down, and for the most part, it should not be necessary to go over that length. And it might not hurt to change the format to one that would also reduce the size of said tracks.
Also, for reference, this is the size of my entire SMBX2 folder (this includes PGE, the game, a folder which contains Custom GFX packs, all the episodes I have and everything else that SMBX2 has) which is not even 4 times as large as your episode.
And the size of my worlds folder which just 3 NSMWXs would almost be the equivalent of (and includes MAGLX2).
For comparison, Airship Attack (which has 170 levels) is only around 180MB and MAGLX2 (with over 200 levels and has lots of custom stuff) is not much over 2GB when both parts are together (as they are when downloaded).
So you should see if you can improve the efficiency of how you are storing your files for your episode by shortening music tracks to 1 or 2 loops, using a format that could make the tracks smaller (if possible) and maybe seeing if GFX files or music/sound files that are used in many levels could be used outside the level folders and just putting them in the episode folder.
If the size does turn out to be necessary and can't be reduced, then splitting the episode into smaller parts to upload should be done to make it easier to download the episode.