i tried to create a own forge server on forge-1.7.10-10.13.4.1558 and I added some mods:
CustomNPCs, backpack mod, Dragon Mounts Mod, Mo Creatures, Fastcraft, Millenaire, Lord of the rings, worldedit
So with all mods exept the lord of the rings mod the server is running totally fine. My Connection is good, no TPS Lags or FPS lags. But If I add the Lord of the Rings mod I get some interval Lags (maybe TPS lags ?) and it is not really nice to play. With just the lord of the rings mod as a single mod on the server it is the same lag like I said.
Well, Idk too much about the technical side of this, but to reduce lag, change a few settings. Turn graphics from fancy to fast, lower biome blende, turn off clouds, entity shadows, and particles, lower render distance and max fps. Makes everything look pretty sucky, but lag be gone