He has a weak CPU, maybe processing the network layer of hamachi is causing more hiccups

MP does some extra work compared to Singleplayer, for instance processing the network information, handling the updates of the other character/player actions, doing CRC updates

Can you try playing through ...

I am hosting a game on my Desktop PC
Specs:
Quad core Intel(R) Core(TM) i5-7400 CPU @ 3.00GHz
GeForce GTX 1060 6GB
16GB DDR4 RAM
80Mbps down, 60Mbps up

Multiple of my friends have no problem with lag on my server but one does.
His specs:
CPU: Intel core i3 5010U 2.1GHz
GPU: Nvidia Geforce 930m
RAM ...