Hi,
I ride to work everyday about 15 miles per target, the road is diverse : road trip , sidewalks,easy gradient , sometimes holes .
This days I ride with a mountain bike to work and i want to make the riding easier.
I've recommendations about buying Fitness bikes : TREK FX 7.3 , yesterday I went to the TREK store to test drive and they offer me to upgrade to advanced model - FX 7.5. They explained to me that they are more quickly and perform better in urban areas in terms of speed and durability.
Also, they presented the following table compares the two models but i did not really understand the differences.
Can you advise me which model to choose and explain to me what are the differences between the models.

Table at :
Bike model comparison - Trek Bicycle

appreciate .