ami7mina World generation time depends on method it uses, obviously, it takes more time if world is very big and if complex data is generated during creation (not only placed tiles into tile layer). Well, 3-4 min generation is not a problem for a sandbox platformer game, as it is intended to be played for not 1 hour, usually. Sometimes you can generate actual world when the player is near to not visited chunks etc.
20k tiles width is a big world, I wish I can run 16k world in total (I am gonna use global simulation loop for tiles to let them heat or cool each other and it must be computationally expensive for worlds 4k x 4k when we add lighting and other systems even if you can move some part of it to GPU).
