My daughter is 19 mths and she has 8 teeth and limited vocab too. she had 6 when she was 17 months too. She did not do anything to gain my attention then. Now she can say Mommy but it started only a week ago. Altho she still doesn't 'call' me mommy. Most of the time when she wants our attention, she would shout in her own language.
Its natural to feel worried when our child seems 'slower' than the rest but dont't worry, i'm sure you know (and many have said) every child is different so it would be best not to compare them (especially if they are siblings). As long as they are active and are generally curious about things, i always tell myself there's nothing to worry about. Hope this helps!