When I was making my map, it seems that constant repeating of execution of the "barrier" particle made my game lag. This is the command for it,
/execute @e[type=!Player] ~ ~ ~ /particle barrier ~ ~ ~ 0 0 0 0 1 force/execute @e[type=!Player] ~ ~ ~ /particle barrier ~ ~ ~ 0 0 0 0 1 forceRun the above command in a command block with "Always Active" and "Repeat". And the lesser the amount of barrier particles, the faster my game gets.
You're running low on memory:
Assign more RAM to Minecraft (see MC-12949). But since you're running a 32bit OS, the amount of more RAM is limited.
Your graphics card drivers are outdated:
Update those using http://support.amd.com/en-us/download
Please report if the issue persists.