How so? I mean ideally the routine that will get you the strongest the fastest is a powerlifting routine. But there is a reason bodybuilders don't do powerlifter routines. yeah it will get you strong, but you will look like a powerlifter too, not a bodybuilder.
if you are doing real training for strength and want to be effective you need rest days and for sure there are no delt days on the menu. those two jump right out as do 15-20 sets.its just not a routine for optimal strength, and does appear that you are dealing with cns or any of the things that go into "real" strength.
you mention changing routines frequently before too. there is no way you can really comprehend a new method within a cpl months.
just using "DC" training as an example as i know it pretty well and ppl often misunderstand it, i would say that YOU wouldnt even be getting to the understanding point until 2-3 months. closer to three.
like mentioned early you havent put the time into you cns necessary, probably not the pain barrier either.
personally i think most ppl waste way to much time in the gym and put too much focus on exercises that are a waste of time thinking they are bodybuilding.
for years i only did one set as a work set per muscle so for delts that pressing, chest as well.
the heavier i work the more rest i need. there is no way you are doing 15 sets to the max, just not possible. all out is all out n you cant repeat it, you can hit the same wieghts for max effort more then once but the first "set" or part is gona have the most reps, you might be able to repeat the wieght but if you actually went all out the first time, the second you are not hitting the same number, and if you keep doing it until you cant move, your cns is fried.
i have seen many a focused powerlifter diet down a lifter and look beastly even in bb terms. so i dont put much into the bb training vs powerlifter training. especially form someone that didnt take time to build a base with strength stuff. that said, it prob isnt the best idea for someone in there 30s to focus on super heavy weight and more traditional power lifting routine, better to keep the reps higher to not get hurt, and for cns recovery.
as an example for "legs" 1-2 sets of squats all out is all you really need for quads. but do that first set to 20+ reps all out and you are crippled.