I’d  agree with what back forty said. 
Presume your talking about an original SE?
I just checked my 16gb SE. Running latest software version 14.4.2, that uses 6.33gb. Apps looks like it’s about 3gb. Media maybe 1.5gb. A bunch of other stuff smaller than that, total of 13.1gb used. I’ve got plenty of apps on, plenty of pics, use Apple Music. I do use iCloud for everything I can.  
I reckon you need to go hunting for whatever media is storing that much stuff on your phone.
A reset helps as well, hold down home and on buttons together until phone switches off and back on again, can take 20-30 ish seconds.