GO GET THAT BAG. (Remember, no refunds though)
The particle system is probably responsible for the lag, unity handles particles really poorly when they are close to the camera and especially when there are alot on the screen, graphic processing, nvida, something something...
PS. someone said that the screens in the background do not match with the aquarium and look out of place and I tottaly disagree (then again, art is subjective, but just wanted to let you know that I personally quite like it)