Indeed Remeron can have therapeutic effect sooner than the SSRIs or SNRIs because it is a serotonin receptor antagonist. Based on personal experiences, I can say the therapeutic lag was shorter than with a particular SNRI too. The catch is increased sedation and appetite stimulation. It a very unique antidepressant in its own kind and I am impressed with the results I get from Remeron but I'm experiencing hypersomnia on it.
I do not get the groggy feeling because I think I am compensating with extra sleep time. If your circadian rhythm hasn't been modified since taking the drug it is very probable you will experience this for a while until you become adapted to the drug.
I don't think a lower dose will cause more sedation, this idea is probably due to it's off-label use for insomnia on 15mg doses.