Game Bugging

I created some maps in superflats worlds with only 'Air' block id. All of them "crash" the game when played for some time, about 10 to 15 minutes. The game don't really crashes, It just don't save and all the players start lagging like if they are on a server with a very slow internet, even the player who is the host. Please, I'm a map maker, and all my maps are with this problem.

I "crashed" the game in 10 seconds just using this command and hitting the PigZombie after summoning:

/summon PigZombie ~ ~1 ~ {Equipment:[{id:276},{id:309},{id:308},{id:307},{id:306}],Attributes:[{Name:generic.maxHealth,Base:999},{Name:generic.movementSpeed,Base:0.4},{Name:generic.attackDamage,Base:-10},{Name:generic.followRange,Base:999}]}