How do you beat level 15 on dragon slayer 2

The only way to beat the boss at lvl 15 is to save up as much gold as you can and invest in a carpenters guild and at least 10 carpenters. They will repair damage done to your castle. Also, try and get a lvl 3 ballista and as many ballista crew as you can afford along with upgrading your castle to stone. Do not waste gold on the hauler as food is not that important this early in the game. Hope that helps.

I haven't really looked into it but if you let the dragon get all the way into your screen before you hit him the first time he usually doesn't do the attack where he kills you right away