You'd only get sweaty if you treat it like a racing bike.
^This, although it may be an oversimplification. Allowing for the weight, which is about half the all up weight of a petite woman, it should still be possible to do 8-10mph for the same exertion and walking at 3mph. The trouble is, if you ride properly on many roads at 8mph, you really feel you're holding up the traffic, which some people are not comfortable about. So they ride faster and get sweaty.
^This, although it may be an oversimplification. Allowing for the weight, which is about half the all up weight of a petite woman, it should still be possible to do 8-10mph for the same exertion and walking at 3mph. The trouble is, if you ride properly on many roads at 8mph, you really feel you're holding up the traffic, which some people are not comfortable about. So they ride faster and get sweaty.