The problem lies in the first sentence which should be
We are film producers - it's a compound noun with the first noun acting adjectivally, so it can't be plural.
First of all :
- One use of the present perfect (the one relevant to your example) is to describe events occurring in past to present time.
- Continuous aspect expresses events which are or were ongoing.
When the event(s) are past and completed (so
not on-going), the simple form
must be used :
We've made 16 films since we graduated from college (= 16 individual completed past events in past to present time -
since we graduated from college.)
However, if there is no indication that the action(s) described is/are individual events, then the two concepts (past/present time and ongoing events) can be combined to produce the present perfect continuous - which in this case can be used interchangeably with the simple form. So here :
We've made films since we graduated from college.
= We've been making films since we graduated from college.
The two, in this context, have exactly the same meaning. The only difference is that the second emphasises the on-going concept more than the first.
Here's another example:
I've had a headache three times this week (three separate, individual headaches in past to present time -
this week)
But
either :
I've had a lot of headaches recently or:
I've been having a lot of headaches recently
(The headaches are presented as an ongoing problem in past to present time)
Possibly the textbook used only the first structure - the present perfect simple - because the present perfect continuous had not yet been introduced. But the simple form is certainly not wrong.
Present per./ present per. cont. 
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