At retirement, there would be
- an owned house
- two owned investment apartments
- 3,800,000 in an investment portfolio
- retirement fund contributions
Not bad from adding an odd job into the mix for 15 years.
Oh boy! ¡Wadda odd optimistic math for a world where nothing unexpected happens!
Yeah! ...there are realities of realities in this world!! 
Which is more embarrassing?
You call it optimistic?
I call doing nothing and expecting something the height of optimism.
Yeah! your math results. I call your math results quite optimistic.
¿How comes anyone could expect accumulate such figures and property possessions without having never spent a single penny throughout the way of 15 years on an obvious plethora of unexpected unforeseen contingencies?
Have you read what you have written? Yeah, go ahead, read it again!
You seem to have skimmed the post.
in a hypothetical scenario where he earns 5000€ from his normal job, has a mortgage, a car payment, utilities and food etc, he saves 500 a month (10%).
He has a job. A good job. He is able to save as well, from the job alone, like most people with a decent job. Unexpected events often happen - regardless of whether you have a good job, additional income, or no job. Personally, in that situation, I would rather have a good job and additional income sources - but you do you.
12x15x500 = 90000€
An extra odd side job stacking shelves at the local supermarket or whatever = Only God knows how much more one can add to the pot.
The eventual %APR revenues & profits from these savings, investments and whatnot = An even harder & wilder unknown.
And all this assuming one can conserve the same well paid jobs during the 15 years and if one is some sort of almighty & omniscient wise investor to make the best and infallible decisions about where to put our money without any potential setback & losses and without have had to spend a single penny of that in anything at all.
So again. How one can expect to accumulate at the end of 15 years the necessary do$h to posses: