Connecting new La Cie Mobile Drive with Thunderbolt 3 port into Thunderbolt 2 port of late 2015 iMac

I’d bet you have a solution. But that unit costs more than my 5Tb mobile drive. So it seems either I bought into the wrong operational idea or the wrong device. Being retired I can utilize the luxury of extravagant waste of time! I shall copy slowwwwwly. Thanks.

I guess my final comment would be that I cannot get any direct claim from La Cie as to the speed of their mobile drive. My recently calculated interpretation of their indirectly expressed claim of speed is that may be as little as 1/3 Gb/sec as compared to my iMac's Thunderbolt 2 port at 20 Gb/sec or my MacBook Pro's Thunderbolt 3 at 40 Gb/sec. So overwhelmingly my boat anchor is my choice of a pretty slow "fast" drive. Since my Thunderbolt 2 is only half the speed of my Thunderbolt 3, I would think that getting the excellent interface you suggest (reviews are good and it does not have the unreliability issues of cheaper alternatives) could still leave me with a 6 hour data transfer if I went with a top notch interface. It is basically tough to hurry a 3 legged camel. Better to have bought a horse! Thank you for a worthwhile and interesting suggestion.

It is the 5Tb Mobile drive now selling (purchased May 19, 2021) on the Apple website. It has no separate power connection so must be powered through the port to which it is connected. Apple Adaptor may be an issue for power? System report on iMac does indicate UP TO 5 Gb/sec on USB 3.0 bus - not AT LEAST lol. You have perhaps settled my issue, making hope of a better speed of transmission unlikely. Cure? Buy new iMac with USB C of course - and contribute to the absolute mountain of computer junk. I shall wait until I can't update the OS which will come far too soon - why I updated my old MacBook Pro. The biggest single thing we could do to help the climate problem would be to make things to last - too obvious and business hostile.