Whatever the max engine height you have is with a 15" vs a 20" mid it will lower the overall motor height by 5"'s. Thus putting the #6 cylinder closer to the waterline. I agree with SS930.
Remember it is all about where the prop shaft is in relationship to the bottom that will not change once you get max height for water pressure figured out.
I also agree 60lbs is a lot. Maybe the 15" version will not have internal Verado steering and they are loosing the steering cylinder also on the front of the motor.

if you loose the internal steering you will need external...what's the weight difference there?

It would make perfect sense that Mercury would offer different versions of this new outboard like they have in the past with the venerable 2.5 Hi performance. It would be cool to see several options that would include a much lighter weight model that could be used by many of us in the19-28 ft category.

I was discussing this with a buddy today, and we think they're dropping that amount of weight by going to a conventional style transom assembly and single ram trim setup with the pump in the boat. I believe the 20" version is using a built-in hydraulic steering system, as well as the 3-ram trim setup that is all in the transom assembly. I agree that losing 66 pounds would be impossible through the mid and a powerhead diet alone. And I had my weight incorrect on the 20" version in my earlier post - it's actually 687 pounds as listed on the tag on the swivel bracket, so after losing 66 pounds the 15" version will still be 621 pounds (not a lightweight by any means, but better).

I have hydralic Jack plates. When i get my boat set for maximum top end performance at the higher positions the nose starts to settle down near 100 and as the transom lifts from this I loose water pressure even with the water ramps on my hull. We will increase my water ramp cut with my mods but I was also considering thru hull water pickups especially if I eventually change to the 400R to allow higher shaft position. I think a single B Bracket for both motors with 15" mids would lift both evenly and allow adequate setback. You could also raise motors to keep lower cylinders safe if thats an issue while off plane.

Thru-transom pickups would be a good idea on your rig Sam - have Chris install them while you're boat's at his shop. If I were after every last mph out of my 28, I'd definitely install them and rig up the low water feeds to the gearcases. I'd say they're probably going to be a must-have setup with the big 400R gearcases.

I have not seen thru hull on a 3.2 outboard Sportmaster. I remember the old 200"s with Bob's nose cones. It would be nice not to have to modify the gear cases as I have spares which would also need to be modified and would kill my resale values.

Where do I start?

Here's a pic of the one on my 21 Trick. The boat already had the thru-hull pickup and the fitting on top of the deck, that's why the routing was a little odd. But look closely at the gearcase - that's where you drill/tap the gearcase for the water line fitting. If I remember correctly, there's even a small dimple at the exact point where you drill into the water passage area of the gearcase. And if you want to sell the gearcase, just put a brass pipe plug in the tapped hole in the side of the case and it's back to normal. Shouldn't hurt the resale at all.

It's official, Your the best resource guy for been there done that on OSO. Thanks Dale!

Are you leaving the low water pick ups intact?

You're too funny Sam! After 15 years and 11 different boats that ran over 100, I certainly hope I learned something along the way! And yes, I leave the low water pickups at the bottom of the gearcase stock. Some guys weld closed two of the three openings to minimize drag - but that's taking it to the extreme.