A quick google tells me, that there is no rtp and that your game should be around 400mb if you include all the assets without compression or removal of unused files. Are your additional files 400MB? Maybe the internet lied to me - again. So I shall do a quick reality check.
https://itch.io/games/tag-rpgmaker-mv
A couple people actually tagged rpgmaker mv. So lets have a look.
153 + web version, 270, 481, web no dl, 379, 188, 277, 116 + web, 112, 153, 400, web , 209, 210
Maybe you included windows and mac version or even html and android in the same archive? Or an accident happened and you doubled the files?
Anyways, I just wanted to illustrate what someone like me thinks when reading the infos given on your game page.