Sad news...... I made a fundamental mistake of not testing my game in as many devices as possible :( :(
Saw it running on a Xiaomi Redmi device, running Android 4.2.2, 2G RAM, 1.2gHz CPU... and also a similar-spec older Samsung Tab... and they are horrible laggy!!! :( :( Have to halt further levels design and reconsider downscaling the resolution - *IF* that is the cause.