Full time workers are able to reduce as low as 50%, but you basically buy leave credits with the prorata salary reduction. So if it was ok from an operational standpoint, you could work 85% and take the summer off. Or you could flex days as appropriate.
Below 50% is a transition to part-time which has other complexities.
Personally, I’d look to make a part time professional in the US a contractor, as the benefits of being a 1099 are probably better.