Is it too late to appeal?

Is it too late to appeal for merit / financial aid the week before decision day? Is there a benefit to waiting this late? My son is deciding between two schools. One gave him 15k, but the other, which is probably his top choice, gave him no aid whatsoever.

Follow up question, if we don’t hear back in time, but we put a deposit anyway, is it possible they will offer additional scholarship / financial aid after the decision deadline?

What kind of music major? Is it an audition based program where merit aid is determine by the strength of your audition?