I'm answering all your yes/no questions with "yes."
1. Yes I can tell you some of the differences
2. Yes it has a different crankshaft
3. Yes it has different pistons
4. Yes ZC and D16 pistons will fit inside the D15
5. Yes the sleeve (wall) thickness is the same
Differences-
The D15 has a shorter stroke than the D16: 84.5mm compared to 90mm. The rods are also shorter, 134mm for the D15 (except D15Z1) and 137mm for the D16. The LS rods are 137mm, so you can swap them out with the D16 (same rod journal size), but you can't use them easily in the D15 (I think still same rod journal size) because your pistons would all of a sudden stick 3mm out the top of the block during compression. You could solve this problem if you use pistons that have a compression height 3mm shorter than your stock pistons. Stock D15B2 pistons have a compression height of 30mm. The 92-95 VS pistons have a compression height of about 27mm. The 01+ Civic pistons are also 27mm.
http://www.heeltoeauto.com/dseries/dseries1.html
Using those shorter compression height pistons and LS rods would theoretically work in your D15- as long as the rods will fit the crank. I don't want to look the rod journal size up right now. You'll have to add a bushing in the pin end of the LS rod to get it to fit the small D series wrist pin too.
The crankshaft for the D15 has a smaller main journal size than the D16, so you can't swap cranks unless you do some machining to the journals on the block.
One option- you might try looking into B16 rods. The B16 rods are 134.36mm long (pretty sure), which is close to your stock rod length of 134mm. If you use slightly lower compression height pistons, like 30mm instead of your 30.70mm (assuming heeltoeauto's page is correct), then you could probably run B16 rods in your block. The LS rods would give you a better rod/stroke ratio though, resulting in higher rev capability and more dwell time at TDC, which = more torque also.
To make it a little more clear in reference to your first question- the bore size is the same between all the D blocks, so all the D series pistons are interchangeable... well, they'll all physically fit in the same block. The thing you're worried about is the total height of the piston/rod assembly. Compression height is measured from the center of the wrist pin to the top of the piston deck. That doesn't include any of the dome or dish material in the piston. Your stock rod is 134mm, and your stock compression height is 30.70mm. Add that up and you have to maintain a total height of 164.70mm. Now you can start thinking about different rod/piston combinations.
LS rod 137mm + PM3 (D15B2) piston 30.70mm = 167.70, too tall
B16 rod 134.36mm + PM3 piston = 165.06mm, too tall
B16 rod + P28 piston 30mm = 164.36mm, should fit
If you look at the P28 and B16 rod combo, you have to worry about your compression being too low... but if you're boosting, you may want that. You'll have to worry about how much the pistons sit "in the hole" and how much the pistons are dished or domed- then you can calculate your approximate compression ratio.
---
There's a LOT more to this, but I'm not going to type a book out here for you to read. Go do some research online- what I've thrown out for you here should be enough to get started... it's enough to make you a little dangerous if you just start throwing stuff together, so be careful.
