Your Travel Agent should give you a breakdown of the $150 fee, and also advise you of the conditions associated with the fare.

The airline may impose a fee for introducing a stopover, or changing an itinerary (or both). Changing the flight to a new date might require booking seats in a higher fare class which will require you to pay the difference. The travel agent may impose additional fees to cover the extra work involved.

Unless you have a breakdown of that $150 fee and understand the fare conditions applicable to your booking class it is difficult to offer any constructive advice.