[Heaven's Night]

Use lotion where the cup edges hit your bust, then keep pressure moderate, don't overdo session durations. I don't know much anything else? Maybe wider foam/silicone rings on the cup edges? I never found anything really good for that, but afaik Noogle silicone rings are quite nice for that.

I got discolouration and edge marks super easy, they lasted ages to be completely gone, some say they don't get them like that, so I guess this is YMMV situation. Fifteen minutes should not be enough to do that unless pressure has been too high.