The problem is you don't want to start the 15 day countdown if you have a problem receiving the email. Yes obviously you'd still have a problem because the countdown could be triggered at any time in the future, but it's still better to not trigger it immediately if you can avoid it.
That said, if the test email bounces, that might be required to start the countdown anyway?
The test e-mail is an e-mail from the registrar to the contact address, so if it bounces, the register is then required to send a real e-mail to that address, which will presumably also bounce. Then the countdown starts.
I have very little expectation that the boneheads who came up with this scheme considered this possibility, and therefore exempted test e-mails from the bounce-trigger requirement.
The imaginary black-hat that hangs out on my left shoulder has already suggested that spoofing a bounce message for a correctly delivered registered e-mail could be used for mischief. Phishing the domain customers is entirely too obvious for him, though the imaginary white-hat that hangs out on my right shoulder seems quite concerned about it. They both agree that black-hat wins this round.
That said, if the test email bounces, that might be required to start the countdown anyway?