Beam Loading Question
There are many questions to ask and I would have to see the situation. Some of the pertinent questions:
1. What is on the floor above? If walls are up there, where are they located? What's on top of those walls? Load path is very significant in multi-story design.
2. How is the beam connected at the ends specifically? The details are very important.
3. An S shape is a very tall and slender form of beam which degrades its performance over long spans. Is it properly braced along its length? Can proper bracing be added?
4. Your deflection over 15.5' should be about 1/2". I get a deflection of 1 1/8", which is about what you had and, as you figured, this is unacceptable. However, continuity and load path will have a big effect on deflection in this case. Is the beam solidly 28' long, or is it broken into sections that are bolted or minimally welded together? If there are wall loads/tubs/refrigerators/etc. above, where are they located with respect to the beam?
5. How is the beam connected to the column that will remain? This connection's details can have a large effect as well.
I have many more questions I could ask and still not be comfortable without seeing the situation myself.
Again, I cannot stress enough that you should get a local structural to take a look at this. You need to find someone that is experienced in multi-story residential design and that doesn't have any ties to your Council. That way you can get an honest opinion and get your ducks in a row before presenting it.