Springtime Lag: Will Port Forwarding Help?

[JupeNupes]

I regularly play with 5 others and max out the player limit. As the game rolls on (maybe ~cycle 300 or so) when spring hits or and particularly when it starts raining I start to see lag. I'm using a wired connection, and so does my friend who is on the same router. We've experimented and saw that it goes away almost completely when my friend on my same router hops off. I think that the problem is that my computer doesn't receive priority from my router over her computer, and I'm wondering if port forwarding will help with that.