It is generally more efficient to cool down on the bike. Use the last km for cooling; ease up on pedalling, dont work hard, raise yourself up to catch the wind. Squirt some water over your hair and inside your jersey and over your shorts and legs so you can cool by evapouration without needing to sweat. Use a wet wrist-band and neckerchief for added cooling. This works better in hot dry but its worth a go in hot-humid conditions.
If you add some ice to the water it should be prettty cold by the 14km mark.