[Android] Significantly Worse performance on better device - 64bit CPU problematic?

Hello. I've recently done started optimizing my game and i've ran into a case where a significantly better device has performed worse. in this case the Samsung Galaxy S6 has been performing on par or worse than a galaxy note 3, but the same is true of S5 and HTC ONE M8.

These underperforming devices share a common feature - they're all using a newer 64 bit ARM CPU. The only device to not underperform with a better CPU has been the LG G Flex 2, which has a snapdragon 810.

The trouble is that i want the game to run absolutely flawlessly [Locked 60] on these higher-end devices yet something is causing issues.

Can anyone help / Offer experience?

Using 5.4.3f1