Please report this to the mod's issue tracker.
Recurrent Complex loaded a new chunk [15, -18] in dimension 0 (overworld) while populating chunk [16, -19], causing cascading worldgen lag.

I have the same issue:

[00:22:55] [Server thread/WARN] [FML]: Recurrent Complex loaded a new chunk [39, 8] in dimension 0 (overworld) while populating chunk [38, 7], causing cascading worldgen lag.
00:22:55.942
game
[00:22:55] [Server thread/WARN] [FML]: Please report this to the mod's issue tracker. This log can be disabled in the Forge config.
00:22:56.010
game
[00:22:56] [Server thread/WARN] [FML]: Recurrent Complex loaded a new chunk [39, 7] in dimension 0 (overworld) while populating chunk [38, 7], causing cascading worldgen lag.
00:22:56.010
game
[00:22:56] [Server thread/WARN] [FML]: Please report this to the mod's issue tracker. This log can be disabled in the Forge config.
00:22:57.214
game
[00:22:57] [Server thread/WARN] [minecraft/MinecraftServer]: Can't keep up! Did the system time change, or is the server overloaded? Running 3004ms behind, skipping 60 tick(s)

Duplicate of #155