Unlikely, mythic weapons are the probably the hardest items to obtain in the game right now. You need 30k Alexandrite (worth about ~150M gil), complete all Assault missions again, get 100k Einherjar points, 100k Nyzul tokens, complete all Salvage areas (that should be comparably easy) and kill the beastmen leaders (this too, probably).

Just the effort you put into it, I don't think it can be done in 1.5 months. Getting 100k ampoules, even if you do it every 72 hours on the dot, spamming the highest tier Einherjar chambers constantly, it would take you about four months. So all in all, rather unrealistic I'm afraid.