On the softer parts split the audio track, normalize the clip, and use the volume handle to set the relative volume. I’d advise doing that before (or instead of) adding a compressor or similar to the entire track… bringing them more into line manually.
If Vegas’s volume handle went up (added gain) from the 0 point like most audio editors you wouldn’t have to normalize but it doesn’t, so normalize the soft clips and pull it down to generally match levels.
After that slap on a compressor if you want. YMMV but I don’t find that automatic levelors generally work as well without some manual editing first.