I'm also about 25 hours in, but there's been decent amounts of times I idled. I usually stick to auto battle every fight and skip all talking.

I just talked to the tree in the forest at this point so a good 25-30 hours seems like a good frame for completing it!

I leveled up to 70s to beat Jess final form. I was low 60s and got demolished. Indeed Lloyd/Chloe/Eileen seem the best Characters to survive. I also use Win but I don't think he is essential. I just like the green hair.

I know it can be killed, but literally I've been auto battling him for a half hour and 99% of my attacks do 0.  I just don't get it why they made it so annoying to fight !