The mathematically rigorous form of the posed question is whether there is an algorithm with run time f(N) for which there exists strictly decreasing g(N) such that f(N) = O(g(N)). That is, the run time is bounded by a forever decreasing function.
f(N) itself doesn't need to be strictly decreasing, but there needs to be a g(N) that is.
Bottom line, no algorithm can have a forever decreasing run time as N increases. An algorithm can exhibit that behavior over a limited range of N, but that's not how complexity works.
> The mathematically rigorous form of the posed question is whether there is an algorithm with run time f(N) for which there exists strictly decreasing g(N) such that f(N) = O(g(N)). That is, the run time is bounded by a forever decreasing function.
Let's say my minimum runtime is 7, and the strictly decreasing bound on my runtime is g(N) = 1e15/N + 7
Rounding the decrease to the nearest time unit some of the time is hardly a disqualifier for "decreasing". (Though specifically they said "faster".)