No word on papers in IEEEXplore from IEEE conference in Sep, 2015? We submitted and presented a set of papers in a IEEE conference last September in 2015.
However, we still can't find ours or any other papers present in this conference accessible via IEEEXplore (papers for 2014 and prior are available).
Since the next 2016 conference deadline is coming up in two months, I don't know if I should submit our next submission, or not due to this incident from 2015.

What do I do? Do I just need to wait longer for papers to appear in IEEEXplore? Or can I contract someone from the conference organizers? I need to decide if I should submit something for 2016 conference or find another venue.
You could contact the program chair or publication chair for an update regarding the publication on IEEExplore.

Delays like this are not too uncommon, however. A conference I attended in August last year had its proceedings published only in March of this year.

I think you can safely submit to this conference again this year.