Impedance matching through via and signal trace of 2 layer board
Another aspect to keep in mind is the return current via. The path the return current takes also influences the impedance of the interconnect. It looks like the red stitching vias around this section will connect ground planes on the top and bottom layers. The return current for this signal will likely go through the nearest stitching via.
Instead of counting on that return current, you might like to engineer the return current by providing a return via (or multiple) next to the signal via. The size and spacing between the signal and return vias will impact the impedance of the interconect. (see page 12)
My 2c on connecting your large trace to the smaller via is it probably won't matter. I think there would be more cause for impedance discontinuities due to the large size of the pad itself, and the via / return via construction.