In recent days a lot of residents have been asking about Grandfathered Sims.

Why are they different? Is there more lag? Does the sim run worse than a regular sim?

Grandfathered Sims are different only in price the Estate Owner pays. A few years ago Linden Labs raised their prices for their Sims and Homesteads. Estate Owners who had a stock of Sims and Homesteads before the increase kept their current rates. When an Estate Owner purchases a new Sim or Homestead from Linden Labs the new pricing takes effect.

That is the only difference between a Grandfathered Sim and a Regular Sim.
Prices that the Estate Owner pays.

Note: If for whatever reason an Estate Owner sells a Sim to another resident that Sim loses its grandfathered status, thus meaning, that the resident would be paying the higher price. The price for the Grandfathered Sim does not transfer from owner to owner.