I doubt this, at least on an actuarial basis. There’s so much long term welfare drawn by immigrants, who are happy to have large families with public support, that I find it hard to believe they are a net benefit to the solvency of Germany’s Social Security System.
What I can believe is that there has been a short term bump in cash-flow, because there are so many of them, and some of them do work through on-the-books employment.
These are immigrants from other EU countries, not the unskilled, unemployable “refugees”.