it's annoying to have to keep 15$ on my card to make sure it's there when the order goes through.
Budgeting and balancing accounts, you're doing it wrong. I don't mean to sound like an ass, but I speak from experience.
Use that as your record, not what your bank shows as "available balance". If your bank has a web interface, use that every day or two to reconcile your "usable balance" against what the bank says - and accommodate for any automatic payments or other transactions that may have hit the account.
I used to keep a spiral notebook around for this and reconciled it against the bank's web page records every day, but now I use Ledger (http://www.ledger-cli.org/) instead of a pen and paper.