Thunderbolt 2 could only deliver a limited amount of power for small external devices - 18V, 550 mA, 9.9 W - according to the Thunderbolt Wiki page. No adapter will change that. Also, the Thunderbolt display was meant to be connected to a computer so it may not put out any power at all.
You can get Thunderbolt 3 hubs that can charge via USB-C and then connect a Thunderbolt 2 display via a Thunderbolt-3 to Thunderbolt-2 adapter to that hub, but it's more likely to deliver 60W vs. the 85W used by the 15" MBP. The CalDigit TS3 hub ($299 list) delivers 85W. The Apple Thunderbolt 3 to Thunderbolt 2 adapter is $49, and that's typically the cheapest one available. So the cost of single-cable convenience is $299 (you'd have to get the TB3-TB2 adapter in any case) unless there's a cheaper 85W charging hub available.