Small

for (int j = 0; j < 16; ++j) {
  std::string s;
  for (auto i = 0u; i < 15; ++i)
    s += 'a';
}
^ This is Faster?
for (int j = 0; j < 15; ++j) {
  std::string s;
  for (auto i = 0u; i < 16; ++i)
    s += 'a';
}
^ This is Faster?

* The benchmark is run under AMD Ryzen 9.

* For the full benchmark code, please refer here.

* For illustration purposes only, see FAQ for more details.