The 3060 Series is 3X6. 15Series denotes the T-Slot dimensions, and spacing.
You must be talking about the 1530 (1.5X3.0)
I am not too concerned with the hardware, as I could always go to metric hardware if need (it still fit's in the slots on the fractional 15 Series).
And I ordered the 3060 before i knew the dimensions were 3.5X3.5, as I figured anything much smaller would not be structurally sound.
Also I did some stress test simulation in Solid Works, as 80/20 has a real nice add on software, that has a lot of the standard extrusions, and hardware.
I assumed a 100lb load (burner, kettle, and wort). Also I did the simulation with heat cycling @ 30C to 125C 2Hr dwell at each temp 2HR ramp up/down (the 3030 failed after 50cycles, but 125C is a lot higher than I think it will see), this is why i went with the 3060.
Also if need be I did design some brackets to fit the stand and shelf, my cousin is a fabricator so he can make them for me pretty easily at his shop, out of scrap SS.