Level 15 may be the most frustrating level I have ever experienced in any game, took me 12 attempts. The problem is that the boss ninja can only be killed with 5 meteors, even after you have the all upgrades to make them cheaper and more powerful, and you can't rely on the towers to freeze/ scare him, it is literally just quick reflexes clicking whilst using the hotkey. But what I found, is that I was using mana for meteors for the smaller ninjas before, and not having enough mana for the boss. Or, you finally have enough mana and almost get him, but he has 1 health and touches your gem for a second. Also found it annoying you couldn't predict which side he comes from, as for about 5 rounds straight he came from the bottom right, so I focused upgrading there, only from him to enter at the top left the next round.
Sorry for the rant, this is a very good game, just a shame about the annoying last level.
Should be an option to buy bins. I had about 30 janitors over 3 floors and it was still a tip, even after I brought the upgrade.
Still, a good game :)
(I also had a women trapped in my supermarket looking for spices for 6 days!)
Beating it on seriously hard is really easy:
-Play the game on easy until you find the helicopter port, and build the helicopter
-Train 5 people to top level in everything
-Pick these 5 people to go to new destination, then pick seriously hard
-You now have 5 decent people that can build, research, raid more. Then just get any farms as soon as possible, and a bar/ church to sort low morale.