Hmmmm...tough call not knowing what equipment that you have for later levels. But if you do have some good armor and units, and a handgun or mechguns with good hit% then I'd say you could do it at around lvl. 80-90. The hardest thing will be beating the spaceship at a lower lvl. Baranzs and Gran Sorcerors will be especially deadly and the Gol Dragon is a huge pain on ultimate. But if played carefully then it can be done, and if you have PSO+ it's also a good idea to try and unlock the tower quests. The west tower has the most gi-gue's of any quest with a couple floors spawning three at once. Hope this helps and good luck!
PSU Character:
Izurei - Level 50 Cast, Rank 10 Ranger/Rank 3 Force (Future Guntecher) - Universe 2 or 15
Izurei - Level 50 Cast, Rank 10 Ranger/Rank 3 Force (Future Guntecher) - Universe 2 or 15