15mg sounds about right for a first timer. Sensitivity to and subjective effects of zolpidem seems to vary a lot from person to person. While not too likely, some people do get very strong effects from a 15mg dose, so it's good you have an experienced friend to do it with.
I wouldn't count on seeing things though. Some people don't get this effect at all. For me, Ambien does feel somewhat trippy, and my vision can appear a little hazy, but I don't ever get the overt open eyed visuals that some people report.
In my opinion, zolpidem is quite fun though. I don't find it very hard to resist sleeping on it, in fact, it isn't very effective as a sleep aid for me. I would liken it's effects to a cross between DXM and benzodiazepines. It has the feeling of intensity and significance I associate with dissociatives, but is strangely anxiolytic at the same time. I also get the apathetic, lessening of thoughts, sorta confused but don't care, state I associate with benzos. I actually find it more interesting and recreational than taking benzos (I quite enjoy dissociatives recreationally though). Some people trip balls on it, while some find it quite boring,so obviously, YMMV. It's worth trying though, you may just love it.
be safe, and have fun.