My 14 yr old 2.5 ton 10 SEER Trane unit must be replaced. I have two story townhouse in the southeast with approx 1450 sqft. Is the ductwork current enough to accommodate 15 SEER unit with variable speeds or is 13 SEER unit better? Should I get ducts cleaned out?
Do I hire professional to evaluate airflow etc and if so how long would it typically take them to do evaluation & at what cost?

Is the ductwork current enough to accommodate 15 SEER unit with variable speeds or is 13 SEER unit better?

If you are concerned with the duct have the contractor do a manual D. That will answer that question.

The SEER ratio has no bearing on which unit is best. The higher number means that it will use less electric.

Once again have the contractor calculate the electrical usage for both units. Then let your wallet decide if it is worth the extra $$$ to get the 15 SEER unit.

Should I get ducts cleaned out?

If they are dirty get them cleaned.

Do I hire professional to evaluate airflow etc and if so how long would it typically take them to do evaluation & at what cost?

Your contractor should be able to do this for you. If he does a manual D and manual J that will tell the tale on air flow and size requirements. Usually the price they charge for the unit and install should include any calculations needed to do the job correctly.