You could manage Casual just fine, it fits the name quite well. Honestly, a lot of the free roleplays really ought to be in casual; the one that you just sent me a PM about is currently casual in writing level (just based on the first two posts), so don't worry.

For threads where the GM says it is high casual or if you are looking at an advanced, try looking at the works of others and asking the GM via PM if your post length is ok, say, by means of sending an example of your work and asking them if it fits their expectations.

On the matter of easily dying roleplays...

Happens at all levels. It really takes a community of players that cares and has a bit of an investment already, interaction... a little community of those you can rely on to get a faster paced game and have it reliable.

Some of them just go horribly slow; sending a few pokes might help. Players (or god forbid the GM in the GM's own pretty much scripted storyline) can lose the "spark" of inspiration, and things fall apart. I have lost the spark before; one time the GM shut it down because nobody was really doing anything at all and the other I arranged my character's death because I lost inspiration in it.