This is a biking forum, comprised of cyclist. My comment was directed at a new rider, a beginner and what they are capable of after 2 short months.
I'll bet that 90% of us could not hold 15 mph on a normal road course over 30 miles today, never mind when we have only been riding for 2 months!
I'm talking about your local big box store mountain bike, which is the bike most beginners would buy. Post a Strava link showing you can do 15 mph now for 2 hours...