I suppose that the "computer lag" can be understood to be a lack of processing power for the alien Barash's "holodeck."

I don’t think so. When Riker is being made to believe he’s on the future Enterprise, he asks the ship’s computer for information a few times (like his service record), and is told by the computer that it can’t answer for a few hours; supposedly due to something Geordie is doing, but actually because he’s not really on the Enterprise.

I think this is the “computer lag” he’s referring to.

I suppose that the "computer lag" can be understood to be a lack of processing power for the alien Barash's "holodeck."

I don’t think so. When Riker is being made to believe he’s on the future Enterprise, he asks the ship’s computer for information a few times (like his service record), and is told by the computer that it can’t answer for a few hours; supposedly due to something Geordi is doing, but actually because he’s not really on the Enterprise.

I think this is the “computer lag” he’s referring to.