Yes the 15.5k is the maximum you are allowed to defer from your paychecks. I believe if you are over 50 there is also a 401k catch-up which is something like another 5k that you can add (one of you old guys can chime in here). The company will match 50% of the 15.5k for a total of $23,250 if you max it out.
Says who? You can contribute $15.5K this year. The company then matches 50% of 15% of your salary. If you make 75K, for example, the company will give you $5,625. This totals $21,125, not $23,250.