Using the Ventev Wallport pd1300 Wall Charger to supply power to the Thunderbolt 3 based Apple 15" MacBook Pro (2018) from 1% battery level, we could see it took almost 553 minutes for the external charger to fill up the Mac's battery using USB Power Delivery. This is a very long time compared to about 151 minutes using the Mac's own 87W charger as seen here.
Once connected over a standard USB Type-C cable, about 46 watts (20 volts @ 2.3 amps) of steady state charging was observed between both the Mac and Ventev charger. After the Mac has charged for 200 minutes, the current started to bounce and eventually ramped down to about .3 amps as the battery almost filled up. The Mac then continued to trickle charge by pulling around 46 watts at random intervals towards the end of charging. To see more details, click here to download the trace captured by the GRL-A1 power analyzer.
Although more time is needed, the Ventev Wallport pd1300 Wall Charger can still provide decent charging to the Apple 15" MacBook Pro (2018). But if you need to charge faster, you should use the Mac with the Apple 87W charger that ships with the Mac and connected using the supplied Apple USB-C Charge Cable (2m) accessory.