Of all things equal, of course, one will be paying a slight premium for the diamonds from T&C. Btw, T&C stones are not GIA or AGS certified. They have their own in house certifications and cutting system.
I think to put a price tag to a 1 carat is too general. Coz the prices can varies for different 1 carat too. Not only the Colour and Clarity will affect the pricing too, but cut too.
For example, a 1.00 carat H VS2 will differ from a 1.00 carat (D-F), (IF-VS1) too. There are just too many combinations and probability. A $15K will probably be able to get an average (or even lower end) quality 1 carat at T&C.
Even at Other shops like Larry and Je Taime, $15K only probably get you something decent, but not best quality. Like D colour, IF Clarity for example.
So really depends on what one is after.
Hearts and Arrow only show an uniform symmetry and nice pattern in the diamond, however it does not affect the shine of the diamonds.
The fire, brillance and scintillation of a diamond is affected the Cut of diamond. Its the details on the specifications (For example, crown angle, pavilion angle, table %, total depth.. etc) that affect it.
I personally like the Hearts and Arrow symmetry too.
The isee2 diamonds at Je Taime definitely has the H&A pattern!