The potential for an altitude bust was clear with this clearance so I asked a plain English question. “Confirm you want us to stop the climb at 15,000’ “ She said “negative ,climb via the SID means you climb to the cleared altitude of the SID which is FL230}.whilst all four of us believed “climb via the SID except maintain 15,000’ “ ACTUALLY meant we were to stop at 15,000’ her last statement cancelled her previous “maintain 15,000’” so our reply (to be clear to her) was “roger climbing to FL230”