MAYBE

Initial complexity problem:
1:	T:
		(?, 1)    f2(a, b, c, d, e, f, g, h, i, j, k) -> f2(a, b, m, n, l, o, g, h, i, j, k) [ l >= 1 /\ b >= a + 1 ]
		(?, 1)    f2(a, b, c, d, e, f, g, h, i, j, k) -> f2(a, b, m, n, l, o, g, h, i, j, k) [ 0 >= l + 1 /\ b >= a + 1 ]
		(?, 1)    f2(a, b, c, d, e, f, g, h, i, j, k) -> f2(a, b, m, n, 0, f, g, h, i, j, k) [ b >= a + 1 ]
		(?, 1)    f2(a, b, c, d, e, f, g, h, i, j, k) -> f300(a, b, m, n, e, f, l, h, i, j, k) [ a >= b ]
		(1, 1)    f1(a, b, c, d, e, f, g, h, i, j, k) -> f2(a, b, c, d, e, f, g, m, n, n, m)
	start location:	f1
	leaf cost:	0

Slicing away variables that do not contribute to conditions from problem 1 leaves variables [a, b].
We thus obtain the following problem:
2:	T:
		(1, 1)    f1(a, b) -> f2(a, b)
		(?, 1)    f2(a, b) -> f300(a, b) [ a >= b ]
		(?, 1)    f2(a, b) -> f2(a, b) [ b >= a + 1 ]
		(?, 1)    f2(a, b) -> f2(a, b) [ 0 >= l + 1 /\ b >= a + 1 ]
		(?, 1)    f2(a, b) -> f2(a, b) [ l >= 1 /\ b >= a + 1 ]
	start location:	f1
	leaf cost:	0

Repeatedly removing leaves of the complexity graph in problem 2 produces the following problem:
3:	T:
		(1, 1)    f1(a, b) -> f2(a, b)
		(?, 1)    f2(a, b) -> f2(a, b) [ b >= a + 1 ]
		(?, 1)    f2(a, b) -> f2(a, b) [ 0 >= l + 1 /\ b >= a + 1 ]
		(?, 1)    f2(a, b) -> f2(a, b) [ l >= 1 /\ b >= a + 1 ]
	start location:	f1
	leaf cost:	1

Complexity upper bound ?

Time: 0.144 sec (SMT: 0.134 sec)