wile1coyote
Hello & Welcome to the Forum!

First thing, I suggest you lubricate the axles on all your cars. It will help them roll easier.
15 cars is a pretty heavy load for a single locomotive & you will have a considerable amount of drag with that many
cars going through curves, thus slowing the train down. 
Your Powermax Transformer supplies 40 watts of power, which should be sufficient power for your single locomotive.  You might want to add a second power feed at the furthest point of your track.
If you have lighted cars, they will use some of the power, cutting down what is available to the locomotive.
You'll also want to make sure your wheels & roller pick ups are clean and your locomotive is lubricated.
Cleaning your track is helpful too.  If you haven't done so yet, you might read the pinned topics in the
Lionel Maintenance & Repair sub-forum.

For your train, you might want to consider double heading with a second locomotive, but that will mean
that you'll want a bigger/more powerful Transformer.
Here's a link to Lionel Transformers and Sales: http://www.lioneltransformer.com/
He has very reasonable prices for his restored transformers & stands behind his sale's & repairs.
He also will take your old transformer on trade in, if you choose, lowering  your purchase price.
(no connection to seller, I do purchase parts from him for my repairs)

Again, Welcome! 
I hope you'll post some photo's of your Carpet Central Layout & Train.

Happy Rails!
Dave