We are currently working on an application that automatically supplies meraki devices (from the configuration of organizations, networks, devices, SSIDs, to serving the "splash page" in the Access Point, one different per SSID of a Network, 15 in total).
We can't achieve a complete provisioning flow since there is no "request" in the APIs that configure a custom splash URL. This can be manually done in the Meraki portal.
For a high number of requests, making that configuration manually would be very impractical, we need detailed information about how you have implemented this functionality in the Meraki portal "https://n174.meraki.com/"
With the network ID, lookup the name/details, then apply custom policies to the client or deliver location specific content.
btw, are you really serving 15 SSIDs on the same AP? This is not a best practice if so. I would consider dynamic splash pages on a single SSID, where possible. Unique SSIDs should only be advertised when they require different association types (open/WPA2/Ent). This will reduce interference by lowering broadcasts, etc.