I used to move appliances up and down stairs alone that weighed considerably more than 155# and some were quite awkward, the 155# will not be a problem - at least weight wise.
Don't most places have stairs to get on stage? Don't people move their 4X12 cabinets (about 95#) up and down stairs and risers with two people no matter how short the staircase or lift is; seriously, the additional 60# should be nothing for two people to manage.
The advantage of this cabinet is that it will be a one trip cabinet and it will likely not "require" two people especially going down stairs, we'll have to wait and see about going up the stairs after it's completely built, the components have been added, and the center of gravity shifts from the theoretical location. I actually solid modeled this entire thing including the physical size, weights and approximate center of gravity of all the components that I plan to add to the cabinet and placed the side lifting handles directly under that completely assembled (including components) theoretical center of gravity, this also allowed me to know where the center of gravity is located when an average 6' tall person pulls this cabinet on its wheels and tries to pull it up a standard 8" riser staircase. I've actually thought a lot about this part of the product because I consider it a major feature and planned ahead as best as I could, but even well thought out plans can come crashing down, that's exactly why we make prototypes prior to committing resources to full production.
P.S. Your 20# guess was actually a pretty darn good guess, all you would have to do is switch a couple of components and that 155# could easily shift 20# either way.