stick with the 30BI or 40BI rule.it helps a lot when you deal AA vs KK hands,or made a bad call or got sucked out.grind 10NL can be a hard run(for me).but i think 15BI rule is pretty tight,and make your bets and calling bets harder(always thinking about the cashier button).i think its better you play 3-tables 10NL then 2-tables 10NL with 25NL one table.Your thinking will be different then on 25NL,you will play differently on 10NL,and you will pay more attention on 25NL 1 table,which then your 10NL reads will suffer.