I've heard a variety of conflicting reports. Some say that the low range of 3-5mg is plenty. Some say that 10mg is a great strong dose. Still others have claimed that 15mg was disappointing.
Personally, I've tried a 7mg dose, which produced a powerful and ominous lucid psychedelic dream but while I was awake it wasn't particularly strong. Physically it was as easy as LSD except with less anxiety. But then, I had some phenethylamine tolerance, so that may not apply to you at all.
I plan to take 12-14mg my next time based on the strength of my last experience and my experience with DOC. Plus, I enjoy the amphetamine high a great deal and have tripped many, many times. But definitely, definitely start low. You do NOT want to be stuck in a DOX trip that's too strong for you to handle.
FYI, the overdoses in the sixties happened, as someone mentioned, primarily because the distributed doses were ~15mg, and people were only used to LSD. DOM comes on much slower than LSD, however, so these people redosed, sometimes more than once, thinking that one was not enough. I doubt a 15mg dose would cause any serious problems for anyone other than potentially mental issues from it being too intense. But I would not start anywhere near that high.