Can standard music system (9 speakers)be upgraded to premium system (15 speakers + 1 sub) in MYJ

Take it to a shop. My M3 had no sub. I'm glad I took mine to one that was familiar with the official Alpine upgrade and their installers are keen on it. After I popped the speaker off the stock sub they installed, ended up WinISD modeling for the perfect driver and couldn't be happier. The hardest part is getting rid of rattles, but that's always been true for me past 30 years of subs in cars.