I experienced a similiar issue. Drop-Down-Menus (like Add Component, or right click on actor in the viewport) wouldn’t open in 5 out of 6 cases. Impossible to work with.
After updating to 4.15.1 the problem disappeared. As this is something I was about to do anyway that was no hard choice, but for others, especially those that are planing to release super soon, that might be different…