I would imagine the differences are speaker independent. For example, if you have an L2 speaker who is near native or at least very fluent, I would suspect that their phonology is closer to native phonology as well. However, for those who are at an entry level L2 they probably have much more L1 type phonology. I am basing this assumption more on the idea of non-native accent and prosody in new L2 learners. I would compare it to learning to do something left handed that you normally have been doing something right handed your whole life. The L2 muscle memory isn’t there so until those mental pathways are more developed and the L2 is more natural the speaker is going to have to try harder to think about each pronunciation more (Or at least have a few hold outs from the L1 that make it hard to achieve the new L2 phonology map). If you look at some studies on 2nd language prosody and rhythm I think this is apparent. It takes deliberate training (or retraining) to learn to add the correct prosody on top of a new L2. I suspect that the same is true with the basic phonological systems as well. - It’s possible that maybe I am over thinking your question or missing what you‘re asking… but from the accent reduction work I have done I think it’s a learning thing more than a general statement.

Going by the distinction between the two interrelated disciplines, one (phonology) is language specific while the other(phonetics) is linguistic universal. This means that where there obtains different sound inventories across existing human languages, the articulatory process is universal, same organs of production, same speech mechanisms. This simply clarifies that L2 Phonology is possible as no two languages have the same phonology

Scientifically proven, while phonetics is universal at the articulatory and auditory levels, a thorough acoustic analysis might reflect the possibility of L2 phonetics.