Hi OP,

Now, I'll assume your main concern is seat height.

Here's the seat height for all three bike;
Y15ZR : 780mm
135LC : 770mm
Nmax : 765mm

As you can see Nmax offers the lowest seat height.

If you're considering on lowering your bike, the Nmax uses a rear dual absorber setup, while both LC & Y15 uses a monoshock setup.

You can easily lower the front side of the bike by lowering the front forks. To lower the rear side you'll need to find lower shocks.

One option you can consider is getting the Y15ZR and lowering the front forks, then replace with rear monoshock with a 135LC monoshock. The Y15 uses a 210mm monoshock, the 135LC uses a 200mm monoshock which is a bit lower.