@bubu,
Tantalizing independence of India was at last achieved and enjoyed at first on 15th August 1947.
Tantalizing independence of India was at last achieved and enjoyed [at] first on 15th August 1947.
1. I don't understand what 'tantalizing' suggests here. As I don't know what meaning you intend, I can't rule it out completely but it doesn't sound quite right.
2. "at first" is reserved more for speech.
Countless martyrs fell prey to the pathetic display of dignity to bring us the smile of independence.
The grammar is all there but the meaning is a bit unclear.
But we are yet to be fit to rise to our feet to hold the sweet canopy our beloved independence.
But we are not yet fit to rise to our feet to hold the sweet canopy of our beloved independence.
With the bitter sweet experiences of the long 64 years, we have reached this day to stand united under the tri colour flag - the life and pride of our country.
[With] Despite/In spite of [??] the bitter sweet experiences of [the] that long 64 years, we have reached this day to stand united under the tri colour flag - the life and pride of our country.
Let's stop here for now, Bubu. These are all mostly suggestions I've made.