4s vs 5s and gearing

OK so i,ve a big question. I,ve sell my RC8 to my brother but i,ve keep my brushless system and i,ve put it back in my Mugen truggy yesterday night, and the setup is, flightpower 5000mAh, 4s, Neu 1515 1Y and MGM16018.
I,am geared 15/46 on 4s, but i,am plan to buy a 5s or 6s this week.
I want to know, if i run my truggy on 5s or 6s, can i leave the same gearing (15/46) or i must absolutly go down on the pinion

I,ve keep the mechanical brake on my mugen, and i,am limit to a 15T on the pinion, i can,t go down. If i want to go down on the pinion, i must remove the mechanical brake and use the controller for braking, and i realy don,t want to do this.

I know if i go 5s or 6s with the same gearing, the top speed will be realy to fast, but my goal is not to be realy faster but it,s to go down on the current.
So if i keep the same gearing, is my current and the temperature will go down and the efficiancy will be about the same or i will reduce the runtime, raise the current and temperature

Thank you!