This theater is like all the others (meaning it has 15 rounds) just amped up with tougher enemies (harder than the last)
This theater is not that bad but if it's your first run through of it you might have difficulty.
if you do you can buy an extra life (up to three but you have to die in order to buy the next one) in the armory to the right that is where the door is located to purchase lives.
Please note that if you fail you can continue from that same round if you forfeit your score, if you don't you will restart at wave one.
If you do forfeit your score you can still obtain the achievement.
Good Luck and Happy Hunting