1515/1y in Revo Lipo Battery Question

I have exactly the same setup than your's, on 4s frlightpower 5000mAh, and this summer, i'll buy a 5s.
I think 6s is too much for the 1515,1Y, and this will push the component (speed, motor, and poor revo diff) to their limits.

I would run a combo of batts except I am just running one battery tray ...what do most people do just velcro 2 batts together on the tray?...hummm I do have two maxamps 5000 3s batts I can use....at what point does the batt weight start to have negative effect on the handling also..