It could be done. Yeast works much faster at higher temperatures and both growth and fermentation produce additional heat. If the yeast was Muntons rather than Muntons Gold, the FG should be around 1.015.
That much lactose is going to give you a very sweet stout regardless.
Remember one unassailable statistic, as explained by the late, great George Carlin: "Just think of how stupid the average person is, and then realize half of them are even stupider!"
"I would like to die on Mars, just not on impact." Elon Musk