I may be answering my own question with some stab-in-the-dark experiments. I’m increasing the Wave Crest Potential Maximum, Trapped Air Potential Maximum, and Kinetic Energy Potential Maximum, each time doubling them and it’s still taking a century and a day to render. But the particle count is going down.
It also doesn’t seem to properly delete the particle system. I have only Foam checked and when I click the button to delete the particle system and bake it again the previous particle system seems to still be in effect as per the particle count when I switch to the particle system tab. So now I’m clicking the box to delete the particle system in the fluid sim panel, then unchecking the Foam box, checking the Bubble box, and then going to the particle system tab to verify, then unchecking Bubble, checking Foam, changing the numbers and baking. Kludgy workaround.
Edit: tweaking those numbers as outlined above is working, but I’m wondering if that’s the best way to do it. Now the foam particles are moving so fast that the blur effect makes them look odd.