World Memory Problem

i`ve created a new world a few days ago, but today i joined it and was so laggy, but my computer got enough space to store it.
After a Minecraft restart, i joined it again, and i was unable to open chests, furnaces etc. After another restart, i joined it, but the terrain did not appereaded.
Here are some specifications of my computer:
Video card: AMD Radeon HD 6700 Series
Processor: Intel Core i3
OS: Windows 10 Pro
RAM: 4 GB

Can someone plz help me?
Also, this applies on Minecraft 1.8.9, not on 1.9.4