This means his heart is beating at 15% the average for a boy his age. So his body is functioning at 15% of the time it normally would be. The winged lion is a mythological creature that resembles a lion with bird-like wings.
Lars Lion (ラーズリオン, Rāzu Rion?) was the Haos Legendary Soldier of Vestroia. She wore knight armor protecting her upper body.