Development became protracted due to the E15K1's advanced features, and the project fell behind schedule. Problems were encountered with the retractable stabilizing floats, resulting in several accidents when the floats could not be lowered for landing, and the system was eventually abandoned, with the stabilizing floats being fixed, and a more powerful Mitsubishi MK4S Kasei 24 engine fitted to compensate for the increased drag.
The prolonged development of the E15K1 was due to its advanced characteristics, which ultimately led to a scheduling delay. The retractable stabilizing floats proved problematic, resulting in several accidents when they could not be lowered for landing, and ultimately leading to their abandonment. However, modifications were made to the stabilizing floats, and a more powerful Mitsubishi MK4S Kasei 24 engine was installed to counteract the increased drag.