If it's not a round number like 1300, 1400, or 1500, I could see Oda ending OP with a chapter that ends in 56.
On paper, 1556 seems the most fitting, but reaching 1456 would already take nearly 10 years at his current pace.
The goroawase for 1456 can be read as "stone" (いし, ishi) and "rubber" (ごむ, gomu). Luffy's laugh is also shi (し) stretched.