Aren't opening transformations a bother? Nearly every character's first transformation lasted longer than 30 seconds. (Yep, you guessed it--dramatic entrances & flashy transformations that put bystanders in "Aww!" ...It's to enhance excitement)
Though, I have to argue with you on several points. I would say Vegeta would win this battle for 3 simple reasons; chances are he'd trained longer in the form, he had more experience in battle, and his Ki attacks were much greater than Trunks'. USS Trunks couldn't damage P. Cell in anyway, shape or form, where as Vegeta was shown putting up a much greater fight, albeit brain power.
Okay, I wholeheartedly disagree here. It wasn't obvious to you Vegeta was only toying with Cell and Trunks?
(Android Saga)
Super Saiyan Vegeta vs. Super Saiyan Trunks
I gotta see where this is going. >< I'm still under the belief Vegeta could've beaten Trunks in any form, any time... solely because of battle experience, smarts & some of the overall greatest Ki attacks.