Look like the 8ch output expander driver is definitely WS2813 capable - check out the description where it lists a few. It doesn’t list WS2815, but I thought the data lines on those were still 5V so I don’t see why not.
I found this thread really helpful for understanding how the driver/expander works. I’m pretty sure that you wouldn’t have to wire it zigzag.
Edit: The screenshot of the expander setup in the thread above shows how you set up indexing into each of the 8 strips that would be wired hub-and-spoke. Even so, the mapper should be agnostic to wiring because you’ll write patterns in terms of x and y, not index.