World generation really slow!

The people from Spigot sent me here.
I noticed a high decrease in performance in world generation. It lags my server badly when people (and also if it's just 1 person) explore new areas or do a random teleport to somewhere which hasnt been generated yet. I disabled random TP but still my server lags sometimes caused by world generation.
Would be nice if someone could investigate and fix it.

Thanks, freaky.