Also... your winrate in bb/100 hands will almost definitely be higher, the lower stakes you play.

Softer opponents means more big wins. It's not the rate in bb/100 hand that improves your BR, though... it's $$/hand, and the reduced winrate in bb/100 hands can still make a greater winrate in $$/hand when you move up... but at the price of higher variance.

If you aren't making at least 5 bb/100 hands at 2NL, then you prob can stand to improve a bit w/o moving up in stakes, but might still see an increase in $$/hand. The trouble is that you may find that you're only break even at the higher stakes, and need to sit lower for a while longer to figure more stuff out while still increasing your BR.

If you move up and find that you're actually break even, but a slight winner, then you may consider depositing more in your account to have a bit more of a cushion on your BR. You may be more comfortable being a slight winner at higher stakes with the opportunity to study this next level of players than a big winner at the lower stakes where you are mostly button mashing.