I guess W1-5 is for Whale Ship missions, 1st part/chapter (aka Slice missions), 5th mission. In other words, the first 80 Whaleship mission on Slice chapter.

And actually, you don't necessary need to be over the required TP for whaleship missions. Currently I'm doing the last Neutralship missions, requiring 1300k TP with ~1060k TP ship. With 100% succes and almost 100% no dead girl during small pests battles. So yeah, it depend a bit of your girls and teams but with a strong ally, I'm pretty sure you can do the 800k mission. And you know... just start the mission. If it goes wrong, you can still close the game tab without stamina loss (at least, if you don't do this too often).