the yamaha is saying it is the lightest in that class, I suppose the honda is at the other end of the class.
your old Johnson was a 2 stroke so that explains why it was light(er).
Yamaha is 1.8L, and the Honda is damn near 2.4L.
If I wanted another 20 year outboard my bet would go on the lighter loaded bigger displacement Honda. The Yamaha has all sorts of high tech to go to crap down the road.
Edit:
I dug a little deeper and the 115 is using the same engine displacement as the 135 and 150. Those three engines have identical weight, the 115 is just turned down.
What you described on the 115 as a toned down 135/150 is par for the course. Of course, it also can work in reverse....take Evinrude. Their 90 is a toned down 115, which is the top of the hp range for that engine block.
As for the high tech crap, almost all the outboards have similar crap all over them. Emission control. CA has the strictest emissions standards in the country, tighter than the EPA's. Everyone is tech-ing up their engines in an attempt to meet increasingly tighter emissions requirements for outboards.
For the OP, be prepared to lose a bit of holeshot and potentially top end speed moving from a 2 stroke to 4 stroke.
I've owned a few Mercs over the decades I've owned boats, never had complaints about them. Never owned a Yamaha but people I know that have them love them. Same with the Evinrudes. Hondas are not seen on the water very often, at least in the area I live....Augusta, GA to Hartwell, GA. (Clark's Hill Lake to Lake Hartwell.) Suzuki's even more rarely seen and usually in low hp versions.
I'd recommend any of those "big three"....Evinrude, Mercury, Yamaha....not only for their performance, reliability but also the deeper dealer infrastructure that exists. But that's just me as I do tend to wander around with my boat.
What's interesting is the comparisons between Evinrude and Merc/Yamaha that have been put on.....tug of war, drag races, etc. From what I've seen, Evinrudes slay both other brands.
(Evinrude E-Tec 2 stroke 150 vs. Mercury 4 stroke 150---really embarrassing for the Mercury):
https://www.youtube.com/watch?v=R6YJYB23QnY
(Evinrude E-Tec 30 and 40 vs. Yamaha 4 stroke 40, Suzuki 4 stroke 40---shot by marine dealer in Australia):
https://www.youtube.com/watch?v=tZvIw83uZgY
(This is an interesting engine....Evinrude 90 HO, which actually puts out 99hp):
https://www.youtube.com/watch?v=2BCcOWnm7zo
Now, I'm no Evinrude homer. I've only owned a handful of Johnson/Evinrudes over the years and no E-TEC's. Have a neighbor with a 21' Bass Cat with a 225 Evinrude on the back....took me for a ride. Damned fast. He loves the engine.
My point is widen your horizons, consider all the options out there. a 115 is a big purchase.
(BTW...this is what I'm currently "piloting", a 2000 17' Javelin Venom F/S with a 115 Johnson on the back.)