515 000 000 km2 makes for a map of something like 16 047 cm by 32 094 cm but that is huge. At a resolution of 300 you would be able to have a document of 160 by 320 cm. That's 18898 x 37795 pixels and by expirience, depending on your computer, is the limit concerning the size. Even with that, you might encounter performance issues if you have a lot of stuff on your map. So that's probably the maximum you can go.