Wow 3 x 5K Screen 🙂
Theoretically you should be able to do that, i mean looking at the bandwidth side of it.
However although i did not test this, i am quite sure that it won’t run in a proper manner. An HD7850 GPU does not have enough processing power for this …
To be able to run (games for instance)
in 2560x1440p 60Hz in a propper manner you would need a R9 390
in 3840x2160p 60Hz in a proper manner you would need something like R9 Nano / Fury X
So to run 3 times 5120×2880 60Hz i would advise to use 3 x an R9 Fury X Card.