Server crashing because of schematic

If you are still using WorldEdit to load schematics then you should consider switching to FAWE (Fast Async WorldEdit) It is a faster, less power intensive way to load schematics.

You can downlaod the plugins latest file here https://dev.bukkit.org/projects/fawe and watch this tutorial on how to use it https://www.youtube.com/watch?v=Fj4DBoWp1ZQ its the same as WorldEdit... just better :}

You can do this by using a wooden axe and selecting two opposite corners of your build, this will select a box around your build.