Apart from taking Minutes to load your island.
it then just LAGS the whole time and you cant actually do anything, not even chat.
More testing needed this time with large numbers of players, you have underestimated server load.
(im no coder or proffesional, thats you but i suspect UNity is capable of running this game, but on your end you need to optimise the coding that deals with network traffic, ie user data packets, send and request)