Dell 15 5518

I looked in Dell's Service Manual for your laptop. It appears that it takes in air from the bottom and exhausts hot air out the rear of the laptop.

Heat and ventilation are issues with pretty well all modern thin laptops. Always use the laptop on a hard surface, never on a bed, couch, pillow, etc.

You might want to do what I did:

I took a strip of lumber, about 3.5 cm. wide x 2 cm. high (1.5" x 3/4"}, and the length equal to the width of my laptop. I routed out two notches to accommodate the laptop's rear feet. The rear of the laptop sits in those notches, propping up the rear by 2 cm. That provides better ventilation underneath the laptop and makes it easier for the fan to draw in air via the bottom vent. 

It's cheap insurance, and also positions the keyboard at a slight angle that makes typing more comfortable. It won't solve a major heat issue, but it helps somewhat.

You can also reduce heat caused by Turbo Boost by changing power settings.
Settings | System | Power & Sleep | Additional power settings | select your plan | Change plan settings | Change advanced power settings | Processor power management | Maximum processor state: set to 99% or lower.
If you set it to anything below 100%, Turbo Boost will not activate, so system will not generate as much heat and you will save battery power.

Some forum members install Dell Power Manager app from the Microsoft Store and choose a cool thermal profile.

The temperatures that you posted are not a problem.