Farm mana prism

If you have been farming on the Xmas lottery then it should be possible to get 2800MP. If not, then the fastest way is to use your apples and farm on the 30AP daily node.

I got >1000 mana prism in 2 days from the lottery

If you clear all daily quests at least once + spend regenerated AP on 30 AP ember gathering [exp card] daily quest + burn all exp card drops + burn all 3* servants/CEs from gacha
I say yes but it'll slow (or even just stop) you progress through the main story because all AP'll go for DQs

farming the lotto is your best bet to get those prisms...you get 46 prisms per box and another 15 for burning silver exp cards. if you are willing to burn the golds as well you get another 30.
I will shamelessly say that i farmed around 6000 mana prisms during this event...

You'll want to die after doing it, but if you farm pretty much non stop and aren't afraid of burning those rainbow apples, you might get it done. The lottery was a huge help if you managed to farm it, I got around 2200 prisms in 2 days, but now that it's over you're stuck with 30AP ember farming, running about 7-10 silver/gold embers per clear. You can see why this will be soul destroying.