FPS ~50% down, when i`m near map into frame

After i add this - ~25% players on my server starts cry about FPS at spawn location :C
10 chunks in graphic config. Tested without maps in spawn - no laggs.
P.S. I have no lags, very powerfull PC, but players say`s that pfs go down from 40 to 2-4 max.

And map loading, when they in frames - is too slow Fix it too.