Why tennis points are counted as 15 30 40 and tiebreak as 1 2 3?

The scoring system was copied from the game sphairistike, which was played by British officers in India during the 19th century. That game's scoring system was based on the different gun calibres of the British naval ships. When firing a salute, the ships first fired their 15-pound guns on the main deck, followed by the 30-pound guns of the middle deck, and finally by the 40-pound lower gun deck.