Python 2, 117 116 bytes

def f(n):r='',;exec"r=[s+c for s in r for c in')('[s.count(')')*2>=len(s):2-s.count('(')/n]];"*2*n;print'\n'.join(r)

This builds the strings character by character, without filtering.

With piped output and input n = 15, this takes roughly 39 seconds with CPython and 8.5 seconds with PyPy on my machine. Memory consumption is 1.6 GB with CPython and 3.3 GB with PyPy.

Test it on Ideone.

Python 2, 117 116 bytes

def f(n):r='',;exec"r=[s+c for s in r for t in[s.count('(')]for c in')('[t+t==len(s):2-t/n]];"*2*n;print'\n'.join(r)

This builds the strings character by character, without filtering.

With piped output and input n = 15, this takes roughly 39 seconds with CPython and 7.5 seconds with PyPy on my machine. Memory consumption is 1.6 GB with CPython and 2.5 GB with PyPy.

Test it on Ideone.

Python 2, 117 116 bytes

def f(n):r='',;exec"r=[s+c for s in r for c in')('[s.count(')')*2>=len(s):2-s.count('(')/n]];"*2*n;print'\n'.join(r)

With piped output and input n = 15, this takes roughly 39 seconds with CPython and 8.5 seconds with PyPy on my machine.

Test it on Ideone.

Python 2, 117 116 bytes

def f(n):r='',;exec"r=[s+c for s in r for c in')('[s.count(')')*2>=len(s):2-s.count('(')/n]];"*2*n;print'\n'.join(r)

This builds the strings character by character, without filtering.

With piped output and input n = 15, this takes roughly 39 seconds with CPython and 8.5 seconds with PyPy on my machine. Memory consumption is 1.6 GB with CPython and 3.3 GB with PyPy.

Test it on Ideone.

Python 2, 117 bytes

def f(n):r='',;exec"r=[s+c for s in r for c in'()'[s.count('(')/n:(s.count(')')*2<len(s))+1]];"*2*n;print'\n'.join(r)

With piped output and input n = 15, this takes roughly 39 seconds with CPython and 8.5 seconds with PyPy on my machine.

Test it on Ideone.

Python 2, 117 116 bytes

def f(n):r='',;exec"r=[s+c for s in r for c in')('[s.count(')')*2>=len(s):2-s.count('(')/n]];"*2*n;print'\n'.join(r)

With piped output and input n = 15, this takes roughly 39 seconds with CPython and 8.5 seconds with PyPy on my machine.

Test it on Ideone.