The rationale ITL would be that the Germans want the space savings that come from a single dual-purpose secondary battery, like the US and French used, but they also don't want to lose the firepower of their 15 cm guns in anti-surface engagements. Hence, a requirement for a 15 cm gun that can do both roles. Of course, the knowledge that it's better to adapt AA guns to ground use than to do the reverse is based on experience that only comes from hindsight, so that's one of the areas where I cheated to let the Germans know more than they should have. The 15 cm flak guns were real however, as the link demonstrates (they just weren't available until 1939).This was an interesting read.
The 15 cm AA guns are a major problem solver for the navy. 900-1200 m/s. Up to 18 km range vertically, what is this horizontally? 30 km?
Basically, they just needed to see the area where a heavier gun did make sense,
The tripple turrets I think is an overkill except on cruisers. Just go for the historical use of 15 cm gun installations and replace some of the 10 cm guns, then it is a huge improvement..
And overall, I am happy to see the appreciation is dawning on the wonders more use of coal would do for the German industry.
The only comment I would make is that this is only possible with 20/20 Hindsight.
A good chunk of it, yes (mostly the giant locomotive works, and the ITL Panzer I and Panzer II with sloped armor, universal chassis features, and the transverse engine mount). However, most of it just requires that someone look at equipment that is in use by an ally (usually Japan), or was used or prototyped by Germany during WWI, and go "Say, that wouldn't be better than what we're using right now, would it?" After all, that's how I created most of this thread- the equipment was largely based off of OTL stuff.