Single-Queue causing lag?

I was playing a 5 player FFA yesterday with some friends and it went well into the late-game. I had about 20-25 military production buildings and every time I went fast through them to produce units the game would lag HARD, even the other people playing complained about it. Is this a normal thing? I'm using to playing on MQ and recently switched to SQ. My PC is pretty okay so I don't think that's the problem.