I have a 15 gallon pot today. I still have to split some of the 90-120 minute boils into 2 pots & merge them later on in the boil. If I had it to do over again I would get a 20 gallon pot!
If your carbonation is lacking then what you are proposing, along with a warmer temp, may help but if the yeast has consumed the residual sugars then all it will do is cloud up the beer. If the carbonation is okay then I'd say leave it be, unless it a Weissbier of course.
Says it has a drain?
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Chill the bottle first to minimize foam. Be prepared for overflow, 'cause it will. Cap it right away on the foam. Or, find a 1/2 gallon growler, brown preferred. They work great for filling off the tap.
Too late for a starter if you're brewing tonight. That would give you the answer. If it was 80-85F & your car was outside in the sun who knows what the temp was in your car. I'd grab another smack pack if it were me.