According to Hemmings Motor News:
Although Mercedes had been hoping for volume production, the Sports Roadster suffered some disadvantages in the marketplace. The mid-rear engine configuration and short wheelbase ruled out any possibility of a back seat, while the 16-gallon gas tank mounted in the car's nose ate into already scarce luggage space. And the price, at 6,600 deutschemarks, was nearly double that of a basic 130 sedan.
Despite the factory's best efforts to promote the 150 as "a spirited sports car" with acceleration that was nearly equal to that of larger, supercharged cars, buyers were not interested. The 150 Sports Roadster remained in the catalogue through 1936, but few were sold. Even Mercedes-Benz doesn't know how many were produced: One record says that 20 examples were built, while another puts the number at five. There is proof of the sale of just two cars, one of which was reacquired by Daimler AG in the 1950s.
The 150 was impractical, especially during the Depression. But it was and is beautiful.
Recently, I watched a re-run of a 2010 episode of Chasing Classic Cars in which classic car-restorer and show host Wayne Carini drove the surviving 150. That had to have been fun!