It's a tale of 2 birds really, you pay your money and takes your choice.
(i) Low welfare turkeys that have been culled, wet plucked, drawn and frozen without hanging and then defrosted require a much longer cook time, can easily be dry and tasteless. One of these 15lb turkey takes 5 1/2 hours to cook. These form the majority of turkeys sold and consumed at Christmas.
(ii) High welfare fresh turkeys that have been culled, dry plucked, hung for a couple of weeks to mature with their innards in a chiller, then drawn before handing over to the customer cook really quickly, are moist and full of flavour. One of these 15lb turkeys takes 2 1/2 hours to cook.
As an aside, the quality of the feed also plays a huge role in the development of flavour. Again, this depends on the welfare regime.
A high welfare fresh turkey costs 4 to 6 times that of a low welfare frozen turkey.