at 30% crit self buffed your way low on crit. You should really go practice your frost and you should see a significant increase in dps.
and ye the combustion part have been explained to you
15k avg combustion ticks means your using combustion on 30k ignites witch is really really low, especially on a fight like jin rokh where there is a damage multiplier. Some of this may be attributed to your very low crit% witch can make it hard to get a proper ignite rolling, but it still seems a very low.
You also only used alter time once on a 4.43 sec fight, should be used twice =) same goes for mirror image.