lowest amount of games is by pretty much playing everyday and getting the 1k free points everyday
if you want to get lvl20 asap idk u need to grind a lot; like at least 60-80 games
Spike rush give you faster xp if you win a lot, if you get good unrated and fast game its nice too.
But the best its to play every day a bit to get the bonus, its so fucking long!