I'd give at least a half an hour to enjoy the trails and views, I wouldn't just go for fifteen minutes.
I would not see everything in 15 minutes. I was just there & walked the trails to see the great river & Mt. Hood view & a sea lion showing off his swim strokes! With the numerous Spring flowers & trees blooming I took more time to photograph them also, so my husband and I spent a delightful hour and a half there last week!
You could walk through quickly in 15-minutes if you wanted to, but lingering for an hour is probably enough for me. There are a few benches but picnicking isn't allowed.
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