I am hosting modded xp lobbies for a select few hours everyday. You can reach max prestige in under 20 minutes and max out all gun levels. To find out more and to book a slot, please contact me on discord. (Ghst#4735)
This is not free currently but is extremely cheap, starting from 5 $// for 10 minutes of lobby time, which is enough to gain 500 levels
My discord is Siberia#8402 or [disallowed website]