Minecraft – How to make fire disappear after 7 seconds

No, this is not possible in an un-modded, single-player game. There's certainly nothing you can do to a map file to force constraints on the player playing it.

Given that people have been playing adventure maps for ages without the special mode, trust has worked very effectively up to this point :-)

I have the same problem, thats why I recommend using a whitelisted server instead. I believe the problem is that one world has to do twice the work, added with the fact that anything transparent adds lag, Minecraft is doing around 4x more work then it is meant to do on a single player world. Either that or stop playing the game on a Microwave ;)