Before you start on me, the furthest I ever got in my flying career was a PPL with a UK IMC
But, if ever I heard "climb via SID except maintain 15,000’ " I'd follow the standard instrument departure to 15,000' and stop climbing as per the instruction issued by ATC which overrules the SID instructions.
Once the OP queried (wanted confirmation of the limitation) the instruction and got the response "climb via the SID means climb to 23,000 unless given a restriction." that, to me, is where the confusion arises, she had given a restriction, quite clearly, stop the climb at 15,000'