With an OG of 1.150, you are giving your yeast a hell of a job...if you're going to use liquid yeast, you will get best results from making an appropriate size starter to be sure you're pitching enough healthy yeast to do the job, you also need to aerate/oxygenate the bejesus out of the pig, use staggered nutrient additions, and degas frequently during primary to get the CO2 out. Warmer temps may help, but if you can get things going at lower temps (high 60's) you will be better off.
To clarify, you started out with Wyeast 4012, then repitched 4632 (dry mead strain)? I don't know much about/have never used 4012, but the Wyeast Dry strain is a beast, has been my 'go-to' yeast for most meads, and it will easily go to 18%...the supposedly "fickle" one is the Wyeast Sweet strain (4184)