i'm not of pc gamer so bear with me.Sounds like a performance issue more than a freeze. There's quite a bit going on with the fish tank and then there's the potential for NPCs to be doing actions. What are your specs? Keep in mind that the more RAM you have, the better, and that dedicated graphics have very little effect if any.
well i'm on performance mode and my laptop is a lanovo with an intel core i3 and it's got 4.00 GB.
does that help?