22yo male, 6'1" 160lb
i've had good results with 50mg diphenhydramine for reducing nausea without clouding the trip too much. fresh-grated ginger/lemon/honey tea is also a wonderful flavor experience that soothes the tummy (pretty much any tea will help; it's partly the teamaking ritual that grounds my body)
oral 2ce seems to have much more nausea than rectal 2ce for me
because of the long duration, i'm a big fan of lower doses (8-10mg oral or 4-5mg rectal) to allow functioning during the day if need be. at these doses the headspace is quite clear and most activities are easy and fun. movies on HBO are great, but commercials on tv are loud and obnoxious. the mild stimulation allows me to perform chores like cleaning or cooking without too much problem, yet i am still able to lay back and enjoy gentle CEVs.
at an even lower dose of ~1-2mg rectal, public activity and conversation are only slightly 'off', and i was able to participate in discussion in a literature class with little problem, just slight mood lift. maybe some attention span modification, but i can't say if it was improved or reduced. thoughts and ideas came easily to mind, but i had some difficulty arranging words in the proper order for sentence formation.
as others have stated, it also appears that bodyload/nausea can be reduced by dividing the dose into two parts (slowing the onset). so maybe try 5mg oral first, then at t+1 another 5-10mg.
edit: the low-dose experiences are alone by myself, at home for the most part, with comfortable things around me (warm shower, cat to pet, tea, etc). my higher-dose experiences (12mg, 15mg) were in a group-dose setting, which can really improve the mood lift if you are able to shoot the shit with your friends instead of silently exploring your own mindfuck. was your 16mg trip alone or with others dosing?
edit again: the best cure for nausea is to have a simple activity to take your mind off your stomach during the come-up. play a card game with friends (UNO is great, keep the rules simple for obvious reasons) or a multi-player video game. in our circle of friends, super smash brothers or mario kart are top choices, followed by dr mario or tetris. seriously, colorful blocks will help you trip ballz!
edit again again: also, if you have a significant other, try to convince them to play in the bedroom with you. 2ce provides amazing tactile stimulation even at the lower doses, and allows me to maintain an erection with multiple orgasms for hours on end. and each orgasm feels like my brain is exploding with fractal colors. if you don't have a SO, try exploring masturbation cuz it's pretty fun too