That depends on what you mean by "better" & also whether or not you using CT LBB2 (standard mass produced commercial drives primarily for civilian use) or CT HG LBB (custom drives produced primarily for military/paramilitary use) 

I would consider the J6 (TL15) to be better cuz' it can do in one J6 jump what the J5 (TL14) takes two to accomplish.

(Using CT HG, it really doesn't matter what TL the gear is produced at except that higher TL's give a greater # of selection options)

The fact that the J5 drive is 'smaller' (takes up less hull space' doesn't necessarily make it 'better', IMO.

It's just smaller. 

While a argument could be made that a J5 'drive *could* or *should* get better 'numbers' if manufactured at TL15 (vs TL14) that doesn't seem to be the case.

For a detailed explanation of that I refer you to Prof Shulashgili's seminal work, "The Transition from TL14 to TL15 & it's Financial Effects Upon the Efficiency of Starfaring", University of Rhylanor, 1050.

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