USB3.0 speed

I am completely new to USB3.0 since I upgraded from 775 last month, however I am only getting around 12-15MB/s transferring MP3 files to a newly formatted USB3.0 flashdrive, which seems a bit slow to me.

I use a Asus Z170M-Plus.

What could be up here? I have the latest BIOS.

What flash drive is it?

It's a SanDisk Ultra Fit 16GB USB3.0. It has a quoted write speed of 130MB/s.