League is lowering my fps

I'd say this is has happened for the past few weeks, but sometimes when I launch up league it will take a while before it actually loads completely. I'll launch it and it will sit on the "L" logo and will load for almost 2 minutes until it finally brings up the login screen. That's not even the worst part. When I go into a game, my FPS will be HORRIBLE and will leave me unable to play. My FPS will be around 15 and not go much higher than that. I've tried to see if it were a one game issue, but it's not, and I even tried restarting the client but once it does it, then it's like that until I restart my computer entirely. This hasn't happened until I downloaded the new client, and even after switching to the legacy one it will still do this. I've tried repairing my game as well and it doesn't fix the issue.