Well, I'm running a Ryzen 5 2600, should be more than capable lol. My cpu usage stays ~10% while playing.
I've played modded nt a fair bit with larger ones like bruce's pack, this is the first time I've run into any major performance issues.
I tried toggling offline mode, which had very little effect. Game felt smoother for the first bit but the lag still picks up hard as soon as I go to the aquatic path or on the vanilla path gets gradually worse first becoming really noticeable in the crystal caves.
Also messing with the water quality options and toggling shaders didn't seem to make any performance changes positive or negative..?