Did the math for you guys. Credit to Desmos scientific calculator. 1500 frags available from event challenges. That is enough for 2/6 talismans. Multiply 750 by 4 and get 3k frags needed past that point. Taking the biggest possible frag gain/level cleared (night city madness at 12 per level) and dividing 3k by that, you would need to clear a minimum of 250 NC madness levels + the event challenges to get 1 full set.
TL;DR: You need to clear 250 NC madness levels + the event challenges to get 1 full set the fastest.