It would help to specify the exact system models you're looking at, since there are multiple 15" Inspiron models and even multiple 15" XPS models if you count the XPS 15 2-in-1. Since you only mentioned specs, if those items are the only things you care about, then yes the Inspiron will give you similar performance for a lower cost. However, saying "an 8th gen i7 processor" isn't a precise comparison at all. Most systems use the U Series processors that are designed to operate at low power. The XPS 15 systems use H series processors that are much faster. And not all i7 processors have the same clock speed or the same number of cores. If CPU performance is important to you, I would go to ark.intel.com to check the specs of the specific CPUs you're looking at. They have a useful tool that allows you to compare them side-by-side.
But more generally, there will be (or at least might be) differences in other areas you may care about. For example, the Inspiron might use a SATA-based SSD while the XPS uses NVMe SSDs. The Inspiron might have a lower-end WiFi card (this might be harder to determine, unfortuntely). The Inspiron system will likely not have Thunderbolt 3 like the XPS 15 does. And the Inspiron will likely have a plastic chassis rather than an aluminum and carbon fiber chassis. But again, since you didn't specify the models you're looking at, it's hard to tell.
I will say that if you're used to a MacBook Pro, an XPS 15 will feel much more like what you're used to than an Inspiron system.