I'm currently being successful using the 10.2 version with only a few problems recently that are solved by an close/open cycle of ArcMap. My use is focused on watershed delineation and a few other tools including HEC-GeoHMS tools that are not currently part of Arc Hydro. I have never used the Level DEM tool.
I'm not on 10.3 yet, but movement to there is inevitable. I can't commiserate with you on that yet. I assume you've seen the Arc Hydro Problem Solvers thread and are familiar with some tricks of the trade posted there that keep the "head beating on the wall" to a minimum. ArcHydro Problem Solvers