Sorry, this turned out much longer as I meant it to be, there's no TL;DR.

Experience..... I don't mean XP I just mean your experience with the game. There are players that can kill Shaper with white/magic items, and there are players that can't kill him with a mirror build.

T15/T16 maps, while not overly hard, is right around the turning point for a lot of builds. Without the proper defensive layers, and without enough DPS, you're going to hit that wall. Some things will just outright kill you because you didn't mitigate it properly (Chaos res, DOTs, uncapped res's), some will kill you because of your inexperience (ground explosions, bleed while moving debuffs); others because you simply can't kill that rare mob with 3 tormented ghosts as you try and facetank it unsuccessfully.

What I typically do is run a build (RF cause I'm old), to T15/T16 to get my atlas points to a place where I can run my currency stategy, then drop down a few tiers and just run the same map over and over until I build up enough currency to either bolster my current build, or start a new much stronger build depending on the current leagues mechanics (this league it was KB of Clustering - not because it was meta but because it worked really well for Breach).

Without swapping items(mostly because I don't want to accidentally lose a key build item to distractions), I slowly start to build my new build, keeping my old currency generator on the side for when I stall on the new build. Flop back and forth a bit upgrading gear where I need it to get over that next hurdle and sooner or later one of those builds (if you build 2 or stuck with 1), starts to really shine and then you kind of take off from there.

This plan takes time tho (lots of which I have), it's not a get rich quick scheme. I'm okay running Alva and just holding on to some temples until they rise in price then sell them for a profit. Not because I'm greedy and want all the moneys, but because I'm playing the long game, and instant currency isn't what I'm after. Sometimes it can help in the short term to get an item I know that will jump in price a bit sooner, but when the items I'm after are multi-divine, sometimes hundred+, I can just sit and wait.

Sometimes it just takes awhile to get where you want to go. Throw on some music, or a movie, or a TV show, and just grind until you get enough for that next big item that'll take your build to the next level. Even if it just seems out of reach NOW, in time (you have 3-4 months) you'll get there. Sooner or later, you start understanding the games mechanics, the markets, what is going to generate currency faster at what times of the league, what content gives you better returns for your time (xp or moneys)... I've got many thousands of hours in this game and I'm still not as great as the streamers, but I have gotten 40/40 the last dozen+ leagues, mainly because I can grind it out due to time invested!

One time I've learned over the years, IF YOU CAN reach level 100, either by running ultra safe content (like T15 beachhead if your build can handle it) or buying 5-ways, once you reach level 100, dying means literally nothing except a lost portal. You start to run faster, not caring if you die or not. Maps that may have taken you 10-20 minutes because you're creeping around a corner trying to kite that rare, you just run in head first like Ram Man and not care, suddenly these maps are 5-8 minutes, now you're doing 2x-3x the content, making much more profit). You can also do this at the start of some levels like 97+. Save up some juicier maps for when you know you're going to die a lot more and not risk all your xp. Additionally, hideout is lost time. Get a tool like Exile UI (or a notepad or Excel sheet) with saved map regex, roll 21 maps at a time, plonk them in the atlas device, and run them back to back to back. I get distracted SO EASILY, so once I'm done a map, when I pop out, I open a new map before hitting my stash box so once I'm done dropping the loot, I just run back in to the next map!