Sudipta
The question posed by you is what is the significance of Durga Puja to Bengali teens. What your teen-interviewees have addressed is, what they enjoy in a gathering of their parents with other families.It's a fun time which should not be confused as introduction to heritage. The observation is true for any congregation, be it Banga Sammelan or week-end long Rabindra teach-ins. 
Teen-dom does not end at fourteen, personalities take shape in high school, firmly establishing as they go to college, independent and liberated.
You will probably find more enthusiastic responses when you pick your subjects regressively from teens to tweens to children.
Of course we should bring our children to Durga Puja as long as they have fun, which I suspect may stop at the ripe age of fourteen.
Amitavada