This is an Inspiron 7537 from 2015.  The system has no support for NVMe at all (it wasn't common in 2015). The only mention of an SSD is as a cache drive -- these are usually mSATA, not M.2.  It also mentions "optional", meaning not all of these support a card-format SSD. If you don't see any M.2 slot, you're limited to a single 2.5" SSD.
I am thinking about upgrading this to a SSD, the model is Dell Inspiron 15 7000 series. (7537)  the general description of this model says it is capable of using a M2 SSD - I've been inside the case before, even under the battery, I do not see a slot for a M2???  If it has a slot and I just missed it I was wondering if it is NVme compatible? This is what I was considering: Samsung 1Tb 990 Pro PCie 4.0X4 M2 internal SSD. Or should I settle for a Sata SSD drive? I guess my question hinges on where the M2 slot is if it even has one.
Does my Inspiron 15 7000 series have a M2 port