There is a much easier and faster option - put FB.Pixel on the site and call the "conversion count" method there.
https://www.facebook.com/business/help/402791146561655?id=1205376682832142For example, the event fbq('track', 'Purchase', {value: 0.00, currency: 'USD'});
But, if you first need to "check the adequacy of the lead", and then only give data on conversions, then yes, you need to do integration with the Conversion API. Offhand, this is a revision of hours by 12-15.
I also want to say that I wouldn't be too hard on facebook conversions and some smart "learning" algorithms they talk about.
By and large, whether you transfer conversions to fb or not, the effectiveness of advertising will not change by itself. Conversion data is more likely to be needed by a marketer who sets up targeting. If so, then you can pass utm_tags in the box, and let the targetologist go to crm so that he can see which tags of which leads they bring (although it’s not a fact that it’s cheaper to set up and train a person than finish the conversion api).