Use the bundled USB-C cable with Target Mode
Can I use the white USB-C cable provided with new MacBook Pro to copy files from my MacBook Pro to another one, even if the transfer rate is poor?
Yes - according to Apple:
Compared with Apple USB-C Charge Cable
The Apple USB-C Charge Cable is longer (2m) and also supports charging, but data-transfer speed is limited to 480Mbps (USB 2.0) and it doesn't support video. The Apple Thunderbolt 3 (USB-C) cable has Thunderbolt logo on the sleeve of each connector. Either cable can be used with the Apple USB-C Power Adapter.
See here for reference.