After Adding a few Clips to the timeline, audio is no longer imported?
Adobe has this concept of "target tracks" in the sequence window.  On the left side of the media locked/unlocked icon is the "source patching for inserts and overwrites".  On the right side of the media locked/unlocked icon is the "toggle track targeting for this track".  When off, the track name (such as V1 or V2 or A1 or A2) is gray and when on, it's blue.

Chances are good that you left those targeting features well enough alone, and the Adobe defaults are to indeed enable track targeting for your tracks.  When track targeting is blue for only empty tracks, inserting a new video clip does just what you'd expect: it puts the new video and audio into unused tracks.  However, if targeting is on for tracks that already have audio, then when you go to insert the new clip does what you might not expect: it just overwrites the audio clip of the targeted track and that's that.  It does not create a new track for your audio.  If you've inserted 15 clips, it's quite possible that you have audio only from the last clip you added, and that it overwrote the 14th clip's audio track which overwrote the 13th clip's audio track, etc.

There's an answer on VP as to how to restore the lost audio clips (Adobe Premiere - Restore Audio to A/V Clip After Deleting).  My answer explains how to not do that in the first place.