Enemy team of Vi's causes increasing lag

I was just playing one for all with some of my friends as a team of Soraka's. Everything was going fine for the longest time, but then a long while after repeated team fights, me and our random started to lag when the Vi's would start ulting in one after the other. It didn't happen at first but it started getting bad at the end of the game where it prevented us from even seeing what was going on in the team fights. This didn't happen when we were going against a team of Vel'koz's earlier so I'm not sure if it was just because of the amount of particles or what.