sure. At speed aerodynamics are by far the biggest resistance to a bicyclist. Weight is a much less important factor on the flats than most people like to think. On hills, gravity becomes a bigger factor than air resitance (particularly when speeds drop below ~12 mph), and hauling your extra weight (and maybe some extra weight on the bike) uphill takes work.
What kind of bike do you ride? There are some fairly easy and relatively cheap things that can be done to improve your ability to climb (a six or seven speed freewheel with a lower gear would be easy, probably, for instance). Practice climbing will also improve your ability to climb.