Problem With Attack Of The B-Team

Hello I have a problem with my server it has installed on it AOTBT i was playing on it with my friend a long time 8 hours a day , and after a time the server started lagging sending me this:
" [Server thread/WARNING]: Can't keep up! Did the system time change, or is the server overloaded? "
I had 0-5 FPS then i lowered the graphics i had the same , i couldn't move.
My pc specifications :
Intel core 2 Duo 3.00Ghz
4 Gb ram
64 bit
And im using in the options in the launcher 2gb usage for it
Thank you.
http://imgur.com/a/RnPh9
Theres my ticks

I have none of these only the world is big, how can i fix this ???? without reuploading the world edited by MCEdit.

So , all the hard work i did will be deleted ?..
this already happened to me once i reistalled the server and downloaded the map , i tried deleting the chunks.. but i couldn't upload the world , i tried uploading it in different browsers im sure that the file name didn't had any special characters and the file type was in .zip and the size of it was 60Mb .. then i tried uploading it ... it showed up error while unpacking package or something like that ...
ehhh
thank you .

Still.... nothing..
i deleted the chunks with mcedit.
its still the same error...
please help