Optimize Aging.15DaysOurStock query for better performance
- Restructured query to start from invoice table with sargable date filter
- Changed DATEDIFF(now(), inv.invoiceDate) > 15 to inv.invoiceDate < DATE_SUB(CURDATE(), INTERVAL 15 DAY)
- Reordered JOINs for better query execution plan
- Allows MySQL to use index on invoiceDate for initial filtering