The Apple 15" MacBook Pro (2018) supports USB Power Delivery 2.0 charging through each of its four Thunderbolt 3 based USB-C connectors which we tested using the Apple 87W USB-C Power Adapter that ships with the Mac. With a completely drained battery on the Mac, we observed a total of about 151 minutes to near full charge with its own 87W charger over USB Power Delivery.
When connected using the supplied Apple USB-C Charge Cable (2m) accessory, the Mac immediately pulled quick changing current to get up to about 88 watts (20 volts @ 4.4 amps) charging from the Apple charger. After the Mac has charged for a bit, the current eventually settled out and started to ramp down after the first hour of charging. During this time, the Mac could also be seen to randomly pull higher current at some point to briefly draw around 88 watts and 66 watts of power from the Apple charger. As the battery almost reached full charge, the current eventually ramped down to about .2 amps. Even after the voltage dropped to around 5 volts, some quick bouts of residual charging up to about 88 watts was observed to happen several times towards the end of charging.
The Apple 15" MacBook Pro (2018) expectedly works well with its own 87W charger to achieve maximum charging using USB Power Delivery. The Mac uses aggressive power management schemes such that even while the charger is connected to the Mac, the current repeatedly goes up close to 4-4.5 amps at repeated intervals.