Can output current of buck current more then input current?
Yes it can have a higher output current then input current.
But let's have a look at your numbers:
 - Input: 17V 0.9A that is 17*0.9 = 15.3W
 - Output: you want 5.5V and 2.75A that is 5.5*2.75 = 15.125 W.
That is lower then at the input so at least we are not violating the law conversion of energy.

Your buck converter then needs an efficiency of 15.125/15.3 = 98.8%.
That however is a challenge, and as far as I know++ not possible for converters of about 15W.

++I have not got much experience with buck converters so I am happy to be corrected.