Response to curse words within the script

In my script, there is a fair amount of potentially offensive language within the dialogue. My teacher has commented on one of my scripts with the following: "The exam specifically states that students should not be allowed to present material that is too offensive/unsuitable for their age - if you include the language in full we will not be able to watch and present it in a school environment"

I have had discussions with various people about this issue, as I believe it is an important issue to raise. Whilst I understand that regular use of foul or offensive language will restrict my audience of the film, but I wish to keep the regular use of it for several reasons. First off, I plan to film some quite graphic scenes which will obviously restrict my audience without the foul language, so I believe it is the lesser of two evils in this situation. Also, my film is supposed to be regular people reacting to a terrifying situation, all of which are above the age of 18, so I believe they would use foul language in the conditions they face.  The BBFC classify a 15 certificate as a film that can: "Can contain adult themes, hard drugs, regular use of foul language and limited use of very strong language, strong violence and strong sex references, and nudity without graphic detail. Sexual activity may be portrayed but without any strong detail. Sexual violence may be shown if discreet and justified by context." 

There is no sexual content, drug use or strong sex references.  There will be restrictions on my film to a 15 because of the violence as a minimum, potentially more depending on the level of gore shown and therefore, I believe I am justified in the use of regular foul language, as none of it is sexist, racist etc nor is it with reference to sexual acts. An article about censorship from 12 to 15 is linked below.
http://www.theguardian.com/film/2010/sep/30/bbfc-profanity-made-in-dagenham




I realise that this restricts my target audience to 18+, but that is who I plan to aim the film at anyway, and as an 18 year old myself, I am completely and legally able to produce and watch the film I am making.