Hello Henrik, I received a reply from the support: "I agree that ListStreamPlot appears to be leaking memory here. I have filed a report with our developers on this issue so that it can be fixed in some future version of Mathematica."

I asked a guy that provided the solution with additional kernels (so the memory leak would occur in another process which is restarted periodically), but he didn't reply to my question: why isn't neither of HistoryLength, ClearSystemCache, ClearAll working? They're supposed to be cleaning memory.