New and need help

Hello everyone i am still pretty new to POEs endgame and i cannot figure out why i am getting 1 shot constantly in T15 and T16 maps. I am not alching them just making them magic and with easy mods but i am still getting destoryed by essence mobs and the bosses.

Any help would be appreciated.

I am res capped and have as good of gear as i have been able to find for myself or make.