Gameplay issue: Howling Abyss lag (I'm clever with names)

Following the guidelines, ARAM is one of my favorite gamemodes, but recently I feel like the amount of lag on the map has skyrocketed. On an average game, I get around ten frames per second with my visual settings at minimum. On one occasion, the match was practically unplayable, because whenever a new minion wave entered the screen or another teamfight began, my game would lock up, leaving me with nothing to do but click frantically in the direction of my nexus and hope I'm still alive when the game unfreezes. I'm pretty sure Twisted Treeline has similar issues, which begs the question of why Summoner's Rift is the least computer intensive map, when it is by far the largest, and has the most going on.