Hi Ivan,
Transfer speed relies mostly on the hardware involved, but we also need to check for possible software issues. What device are you transferring files to? When transferring via USB connection, is the recipient device plugged into the USB 3.0? Does the device support USB 3.0?
We recommend that you check for and install updates for both your Surface Book 2 and your peripheral device. You can use the Software Diagnostic Toolkit available here to check for software issues and get the latest updates for your Surface Book 2.
In case you need more help, kindly update the post.
Regards.