They make a 1.5 ton condenser unit and evap. coil.
I don't think the contractor is trying to rip you off. 1/2 ton difference is very minimal in pricing.
Ask to contractor what he is willing to do if the system short cycles on the hottest days. He may be able to dump a small supply in another area of the house?
Do you have humidity issues in your location. What part of the country are you from? Maybe the pros can give more info as to proper selection.