I don't know where you got that number, but it's wrong. A 5-person asylum family might get that much (depends on age of kids) if they don't get anything as materials and there is no reason to deduct anything. (Giving things vs money is debated a lot, currently it is swaying back to handing out things and less money)
>and while your average syrian immigrant gets 1500euros
That's nowhere close to reality.
Firstly, an "immigrant" will not get anything. They will get deported if they're not deemed a refugee. Most asylum seekers actually don't get asylum.
Secondly, if they end up getting refugee status/asylum, then they will receive about 300-400 euros a month (that's somewhere between 330 to 440 USD a month for the international crowd in here).