Are talking about having two different products, right? But it would be the same description etc.
OR:
Versions - 1.x - For PrestaShop 1.5
Versions - 2.x - for PrestaShop 1.6 (check "Major update" )
Is that right?
Cause i have customers who bought module (version 0.1.x) for PrestaShop 1.6 and i don`t want them to pay again.