At the time of Nero Egypt had 7.5 million men:
This country is extended as far as the Ethiopians, and Arabia the Happy, and borders upon India; it hath seven million five hundred thousand men, besides the inhabitants of Alexandria, as may be learned from the revenue of the poll tax; yet it is not ashamed to submit to the Roman government, although it hath Alexandria as a grand temptation to a revolt, by reason it is so full of people and of riches, and is besides exceeding large (Works of Josephus, Wars of the Jews 2.385)
As far as I know there is not any historical record of any census done in Egypt at the time of Thutmose II (around 1500 B.C.), which is the time we are probably speaking about. Those who do try to 'guess' at ancient Egyptian populations do so based on “estimates of cultivated area and yields” of the land (a). In other words how much land did they seem to occupy and how well would that land have supported a population. Different people make different guesses with a range of around four million variance.
Now as we have a record of 600,000 men leaving Egypt and just for the sake of argument we estimate the 7.5 million Egyptian men were ¼ of its size at that time (for this is really only guess work anyway) we would have around 2 million men. For the sake of skepticism we reduced this some more to around 1.5 million men 1500 years before Nero, then still the Egyptians would still outnumber Israel.
In any case it would seem that Egypt had more men than Israel at any time in the guesses and when we consider what the scripture says as to why the Pharaoh began to deal cruelly with the Jews, it seems that the number 600,000 makes a lot of sense:
Then Joseph died, and all his brothers and all that generation. 7 But the people of Israel were fruitful and increased greatly; they multiplied and grew exceedingly strong, so that the land was filled with them. 8 Now there arose a new king over Egypt, who did not know Joseph. 9 And he said to his people, “Behold, the people of Israel are too many and too mighty for us. (Exodus 1:6-9)
It seems that the men of Israel were starting to compete with the numbers of Egyptians so that Pharaoh was worried they would overtake them. Therefore the number 600,000 seems realistic and there is no apparent exaggeration from my point of view.
If I were trying to reconstruct the population of Egypt at the time of Moses I would not bother with supposed "land yields" (this is a sketchy science at best) but just start with a reliable figure like 600,000 Jews. Then I would make a rough guess on the biblical description that the Egyptians were 1.5 to 3.0 times that (900,000 - 1,800,000). Then we would be saying from 1500 B.C. to 30 A.D. the population grew from around (1.5 - 2.4) million to 7.5 million. There is nothing surprising or unrealistic about this sort of growth at all. If there is supposedly someone who thinks they can with confidence calculate different numbers, I would like to see the calculation and review the assumption they have made. I am confident anybody could easily find huge holes in them.
(a) Life of the Ancient Egyptians by Eugen Strouhal, Deryck Viney, Werner Forman and Geoffrey T. Martin (Nov 15, 1992) Page 134.