The heap pretty much is where you can request memory from at runtime. Its limit is about 1.4-1.6GB, you have to stay below that. If your heap usage after code compiling is 740MB with a nexus of 500MB then your code uses 200-240MB or so I think. When you publish your game and run that process you should have additional ~200MB to work with then.
"Falls das Resultat nicht einfach nur dermassen gut aussieht, sollten Sie nochmal von vorn anfangen..." - Manual
