The 115 has the same shock length but uses the full 45mm stroke instead of the 37.5mm on the SB100.
Naturally, you’d need more air and pressure for the short stroke SB100 to achieve desired sag. The 115 would need less air to achieve the same sag number.
Kinematically, the bikes should be close to identical. But on a 115, the longer a longer stroke shock and longer fork would make it more plush and the 100. The 115 would pedal less efficiently by virtue of having a more plush suspension.
You can, of course, run less sag on the 115 to make it ‘feel’ like the 100.