Have you seen performance tips
in the manual?
How big is your game? 1.2 GB is insanely big! I never thought that would even work in a browser, I'm amazed if it does!
Mobiles tend to only have 50-100mb memory free if you're lucky, so downscaling artwork isn't going to help make a game that big work on mobile. You'll have to redesign your game to work on mobile and scale it down a lot. You should be testing on mobile from the start of your development to avoid situations like this.
We have plans to add features to load large games in segments per layout so they don't use so much RAM, but we have a long todo list, and if single layouts use a lot of RAM it might not even help.