With only 1.5% culture, the whole dough is closer to a 'washed starter' (plus salt) than anything else. When I'm building a preferment for bread (20-40% of final dough flour), I inoculate it with 5-7% (preferment flour weight) of 'mother' culture.
It's the purpose not the process that defines a preferment. With only a couple %, it does not add a meaningful amount of flavor, so calling it a preferment is nonsensical. It's simply inoculating the dough.
I would agree... it's a common technique in bread baking (yes, I know...
) that *less* starter (hence a longer fermentation of all the flour, and a greater buildup of organic acids) will result in more flavor, and a large amount of preferment (with the resulting fast rise) means less flavor contribution from fermentation of the dough flour -- the major flavor contribution is from the preferment only.
The 'jug yeast' concept applies nicely, but aside from one old post on The Fresh Loaf, I can only find bourbon references. http://www.thefreshloaf.com/comment/107137#comment-107137