Soldered RAM in macbook air 2015
From the images at iFixit.com, you can see that the RAM, soldered directly onto the MBA logic board (4GB of RAM in orange outline,) is not soldered onto a RAM carrier as you would find in a computer with removable RAM. I have no absolute proof, without diving into arcane documentation, but I'm sure Apple has designed the RAM to be interleaved if that is the technology they are using.