I'm sorry i didn't meant to sound too aggressive there, but if my understanding of dymethazine is correct (and i could be wrong i don't know much about it, haven't seen much feedback either) then it isn't as well suited for pulsing as other compounds with shorter half lives. Superdrol is particularly suited to pulsing because the half life is ~6 hours I believe, which is relatively low. This makes it easier to spike blood levels and still get the compound out by the end of the day in order to minimize shutdown, which is the entire point of pulsing.
I think it will still work fine with dymethazine thouhg.
I wouldn't taper because a few weeks into the cycle, you're going to need the higher dose to make gains, especially on a pulse where higher than normal doses are usually utilized in the first palce. Secondly, the steroid is still powerful enough to shut you down whether its 15mg or 30mg. Going to 15 probably won't lead to much anything in the ways of recovering natural test production, so just keep it at 30 and do PCT.
Don't worry about your HPTA, that's what PCT is for. Coming off a pulse cycle will be easy.