I charged my 2018 15" MBP with a Anker 30W USB C charger. While using the MBP the 30W slowed the drain. Then when I went to bed the charger charged the MBP while I slept and was at 100% in the morning.
So it can be done if you can live with the unit draining while you use it, and have long times when you do not use the system.