And it's not "just" about more successful breeding.
The April 15th start date SAVES a ton of longbeards from being slaughtered by non-resident hunters who were abusing TN's early start and (until recently) 4-bird limit.
Most of the non-resident hunters coming for TN's early slaughter were avid, highly accomplished turkey hunters; many of the kind who could easily take 4 long-beards in a single week of hunting.
Delaying the season 2 weeks has greatly reduced this slaughter because this particular sub-set of hunters is going to be turkey hunting somewhere the 1st 2 weeks of April, just now not in TN.
The big problem WAS that most states were opening later than TN, so TN was a huge draw to non-resident hunters. It still is, but we're now on a more level playing field with many other turkey-hunting states. As prime example, we were opening 2 weeks earlier than Kentucky, and our spring limit was 4, while KY's was 2. This difference brought a ton of avid, accomplished turkey hunters to Tennessee, killing disproportionately a lot more turkeys than resident TN hunters.
IMO, the TN turkey season now opening mid-April is a much "fairer" date for resident TN turkey hunters. Non-residents are still welcome.