Switching from hybrid to road bicycle
Road bike sizing seems harder to get right than more upright bikes. Your dealer may be right, but only as a starting point - that's a good size to test ride first. If your dealer wants you to buy the next size down without trying it first, you don't need a new bike, you need a new dealer. 

You have to think about your goals. Road bikes are more aerodynamic and therefore more efficient. So you'll get less exercise for the same distance, or go further in the same time. You may want to go further if you enjoy it more.