I just went looking at one and I don't see any specifications that would lead me to believe it works with TB2 at all. Some TB3 docks work fine with Apple's adapter, but I've had one in particular that was inconsistent and presently doesn't work at all in spite of being used for a month.
It was the OWC TB3 dock, and they were nice enough to point out they don't claim compatibility and that if I needed something cross-functional they've got a dock that would be supported in both configurations but I'm not sure eGPU even works well enough for TB2 considering the constraints on bandwidth and available lanes, I took a look at at as an option but from what I saw I didn't see much of a reason to go that way.