As you deploy RS485 (or CAN) on larger distances you will need to increase cable quality and lower baudrate. For 15 meter I don’t fuzz, I just twist a pair of cables and hook them up. A good advice is to have standard colours for A+ and B-. For better cable quality you can use a shielded solution like illustrated above.
Twisted pair Shielded cable is quite common and don’t cost to much. Just remember that the shield should be connected to ground only on one side of a cable to avoid creating a ground loop.