We cannot create and store tiles up to level 17 for the whole world. Most of level 15/17 is not accessed by users anyway, see https://wiki.openstreetmap.org/wiki/Tile_disk_usage
Instead we can generate tiles in level 15/17 on the fly for less popular regions (e.g. anything but selected countries and cities) and store them in a cache.

• Create a tool to generate tiles on the fly (done)
• Optimize for to be expected behavior: Many simultaneous accesses to neighboring tiles
• Add some tile cache clearance automation
• Integrate things into tileserver-php
• Test on tile-builder, move to darwini