Storage Sense says I have 15gb in Other

[canonuevo]

Hello, I was wondering if anyone can help. I am trying to free up space on my SD card and I have it plugged in to the computer. I do not see the 15 gb that's being taken up. Does anyone know how/where I can delete this?

Edit: Also, does anyone know what the .thl and .thm file extensions are in Photos?