There are many bug reports out there about issues with Dell's TB15 and TB16 Thunderbolt docks under Linux, but at least some of those remaining issues should be cleared up by a pending fix.

A Phoronix reader who has been affected by the Dell dock issues under Linux pointed out this patch addressing poor USB Ethernet performance when connected via a ASMEDIA ASM1042A xHCI host. From the patch, "bad performance was manifesting in Web browser use (like download large file such as ISO image). It is known limitation of ASM1042A that is not compatible with driver scheduling, As a workaround we can modify flow control handling of ASM1042A. The register we modify is changes the behavior."

That 68 lines of new code to avoid packet corruption should yield a much better Ethernet experience with the Dell TB15/TB16 docks and potentially other devices too.

As of writing that patch isn't yet in mainline Linux Git for v4.13 but the patch is being copied to stable so will hopefully make it to the stable Linux point releases in short order.