Correct, there is no M.2 support in this model.
Also note that while it is often possible to mount an SSD in a caddy in place of the optical drive, that drive will be storage only - it cannot be used to boot the system in most cases.
Welcome to the Dell Community @Jester99
Sorry but I think you can use one or the other but not both.
One M.2 slot for Wi-Fi/Bluetooth
Hard drive or solid-state drive:
One 2.5-inch hard drive or M.2 solid-state drive (SATA)
Inspiron 15 3000 Setup and Specifications:
Do you have a CD/DVD installed???
If so you could try using something like a 6DP4N.