Cant play until about 1 minute passes

I play league on a pc that is not new. My pc is about 3 years old, and i run league on a solid 45 FPS and 60 ms. Ever sence the update adding TFT when i get in champ select for a normal game or get into a TFT game i have to wait a solid full minute with 00 FPS and 60 ms until finally poof my fps shoots to 45 and everythings good. I have never had this issue and dont understand why it would happen in normals. Someone please explain!?!