(First thing first, très=very and vraiment=really,truly) Well, 'content' is more like short-term happiness (like if you got a promotion at work or something) and 'heureux' long term (if you achieved your dream, have the life you wanted to have or at least learnt to appreciate. 'Être heureux' would also be defined by French people as 'épanouissement' So yeah, both 'être content' and 'être heureux' can be translated as 'being happy', depends of what you mean by it.

Je suis vraiment content/heureux = I'm really happy Je suis très heureux = I'm very happy