at praça xv, bus 354 stops underground, in a tunnel not far from the terminal hidroviário da praça xv & estação das barcas, the boat terminal.

there is a boat that leaves praça xv every 30 minutes and reaches praia de charitas in 15 minutes. 

from charitas, the bus line 33 goes along the shore and stops at praia de salinas, praia do cais, and praia de jurujuba (final stop).

praça xv is easily reachable via taxi in 15 minutes, or via several buses routing along copacabana and ipanema, including bus 354 - the metrô station estação carioca is about a 10 minute-walk away from praça xv.