You can't actually change the game speed in multiplayer, besides the usual game income speeds etc. at the start of the game.
What happens in ICO multiplayer is that the game uses a lag prevention algorithm that for some reason, increases the game speed as a side effect. The greater the latency between players and the server, the worse the effect is.
Typically this is very noticeable early in the game but goes back to normal as the game goes on.
There isn't anything you can do, other than trying to improve your connection. As an alternative, you could try to do local LAN multiplayer, I'm not sure if the same mechanisms are in place there.