To be pedantic, 1.5e8 carries additional information about accuracy: $150,000,000 ± $5,000,000. By contrast, 1.50e8 would be ten times as accurate, and so on.
On the other hand, if you had said "Pi is 3", you would have been accurate, but not very precise. If you said "Pi is "Pi is 3.14", you would have been so precise that you could have gotten to the moon and back.
At the very least keep it to multiples of three, as in 150e6 or 150 * 10^6! Though a very simple 150 million is easy to think of in terms of erasing past donations that sounded impressive.
Was it really necessary to type it like that?