Part of the Lucky feat (PHB, p. 167) says:
You can also spend one luck point when an attack roll is made against you. Roll a d20, and then choose whether the attack uses the attacker's roll or yours.
When using the Lucky feat to reroll an attack against me, do I add any modifiers to the reroll?
Say the attacker's roll for example is a 23 (1d20 + 6 (prof. bonus + relevant ability score modifier), with a roll of 17 on the die); I use Lucky to force a reroll, and there's a 15 rolled on the die. Do I add the attacker's proficiency to the 1d20 that I rolled for the replacement? Or do I keep it as it is, as 15?