It seems that Dell monitors (in general) seem to have DisplayPort cable issues. I would suggest first finding out what (if any) DisplayPort cable comes with the monitor and if one does, then find the adapter needed to connect that cable to your MBP (it'll either be USB-C to DisplayPort or USB-C to Mini-DisplayPort) . Take a look in Amazon or in other sites to see if people were able to use the cable/adapter with the Dell model you have.
Interestingly enough, I looked on Dell website at the P2715Q, a monitor that interests me for a possible future purchase and there was no mention of any cables included. But a search of "Dell P2715Q included cables" came up with the B&H website, which says that it included a DisplayPort-to-Mini-Displayport cable. Because the P2715Q has both DisplayPort and Mini-DisplayPort ports, one could get a USBC-DP or USBC-MDP adapter. I think a little research on your end will save possible frustration later.