Obviously you can buy juice and have premier membership to help the speed of leveling.
the fastest way to level is to do the following.
First thing is to create a situation where videos lock up. So turn on "Limit Ad Tracking" under advertising.
With this on you will only be able to watch 7-15 videos maybe less for credits then it will lock up and say no videos available. If watching for credits you'd have to reboot the app or reset the Ad ID in order to start watching videos as long as hadn't reached the 150cr/ day cap.
In this case we actually want them to hang up and not be available.
Then on mobile and maybe PCEA. Play one hole coin games. Rio or Tokyo depending on coin counts. at the end of each match choose the watch video option.
now what will happen is you won't actually waste the 30 seconds watching the video. it won't play due to "not available" but you will still get the XP credit. This will net you around 1300xp/hour in ad xp. and another 600+ in game XP minimum. So ~ 1900-2k an hour in xp.
I would also chain apparel runs while doing this to get the apparel you might want leveled at the same time. To support the credit costs can watch the videos but as a legend and if you have some skill I'd play every ready go Legend tier every day that was available.
If you can finish top 10 most of the time this will support your sponsor rounds as well as XP juice.
Im basically describing what I did. You can make enough credits to support the habit. It's just if you want to take that route.
Depending on how much you play you're looking at probably 2-4 weeks per level. can be done faster if you play more.
PS and keep your daily streak up. I let mine lapse a long time ago because levels stopped having meaning. but until you hit 102 don't let it drop.