Scrolling the Registry I found the following key:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows
NT\CurrentVersion\SystemRestore\cfg

In the right pane there is a dword value "DiskPercent = f (hexadecimal)"
which sets the amount of System Restore to 15%.

Question: is it possible to adjust the System Restore size permanently by
changing this value?

Thanks,
Jurij Vega