One thing I've noticed about the TD150 players I've had over here is that they have the lightest/shortest of the Thorens suspension springs in that era. This in comparison to the TD160, its successor and the TD125 which has a very different spring rate. Sorry I can't give precise spring rate data between the three models but when compared side by side, the difference is apparent.
Also, the Td125 uses a much more solid and heavier sub-chassis than does the TD150. So That model should accommodate heavier arms better than will the TD150.
Even the SME 3009 SII improved is a heavier tonearm than is any of those Thorens tonearms. On the Td150, with its suspension designed to carry a TP13/TP13a, any other arm one can think of will likely be heavier than the stock unit.