There is no "optimal" VPIP that you can cite for all players. First of all, style is an important factor, and playing within your own will cause you to have a different VPIP from what some say is optimal.
Also, if we could define an "optimal VPIP" it would depend on a number of factors including, but not limited to the site and limit you play at. Additionally, your VPIP should differ from session to session or table to table since table dynamics should affect your ranges somewhat.
However, at very low stakes like 2nl, tight is usually right, so I would say anything as low as 10% (with about 8% PFR) CAN be profitable. However, I would also say that going a bit higher to about 15% (with a PFR around 13%) is probably going to increase your profitability, since at those limits, you will still see people paying you off with very bad hands.