I am in Hershey once a month for business and fly out of MDT. It is one of the most convenient airports around and is worth any upcharge for using a smaller airport with limited LCCs. From Hershey you can get to the airport in 15 min and it take mo more than 3 - 5 min to clear security...unless there is an Allegiant flight going out. If you have pre-check, it's no problem. Driving to Philly at 3pm is not advised. You'll make it to King of Prussia quickly and then spend at least another 90 min getting from there to PHL. Another, convoluted option I have done is my planes, trains and automobiles scenario...

Uber from Hershey to the Amtrak station in Middletown. Amtrak to 30th Street Station (1hr and 15 min). Taxi from 30th Street Station to PHL (no more than 20 min). Sounds complicated but it is fast and more relaxing than driving from Hershey to PHL.