Hello Pink and welcome to
Symi Chat.Sadly, I think it's unlikely you'll get to Rhodes in time for the 3.30 ferry.
In principle, it IS possible but everything would have to work perfectly and given the number of variables involved that isn't very likely. The flight would have to be on time or early, the Rhodes baggage handlers would need to work unusually fast and your bags would have to be the first off the belt just to have a chance of being out of the airport by 14.45. Then you need a taxi driver willing to get you to the harbour fast and I wouldn't recommend asking the driver to get there quickly, I did that once and had the most terrifying ride of my life! Exhilarating, but very, very scary. And I missed the ferry anyway.
You didn't say whether you are travelling independently or with a package tour company. If you are independent then save yourself the stress, book a hotel room on Rhodes and relax when you get there. If you are on a package holiday the company won't attempt to get you to the afternoon ferry with such a tight schedule and will have already arranged accommodation on Rhodes for you.
Once you are settled in Rhodes and freed from your baggage you can have a wander around and I think you'll find it isn't such a bad place to spend a few hours and one night. Sure, it's not Symi and probably not somewhere you would choose to spend a fortnight's holiday (I certainly wouldn't!) but it's not all that bad.