@superkew, @MACPK: read these two blog entries:Image compression in Construct 2Spritesheets in Construct 2
Construct 2 already does some pretty sophisticated PNG recompression on export. I cannot imagine that a web service like tinypng.org would be able to improve on this significantly at all. Are you sure you have PNG recompression enabled when exporting?
Construct 2 already spritesheets on export in a way that maximises the tradeoffs between file size, memory use, and download time. I'm not sure the problem is with C2; perhaps you could ask @Ludei if they can do anything to improve the load time, such as alternative compression settings.