There is no reason to be using either of your options on your size tank. HOB's are an unnecessary expensive. So are Canisters. If money is something you don't have a lot of to spend, get a Hydro Sponge Filter or a Deep Blue. Either of these are great, just make sure to get one rated for your system.
Be sure to spend just a bit of money plants. If you don'tThey will help things along greatly considering you are running something simple like a sponge.
Hydro Sponge II is rated for up to 20. You can pick them up online base cost for 7-10 USD on average (plus shipping) online. Deep Blue Sea is another brand and it is popping up in more and more stores. I prefer this brand due to it being easier to do a quick disconnect versus the Hydro for when you clean it. Some people claim sponge are messy to clean when you pull them out. If you take a pitcher and use it to cup the unit when removing the sponge you can prevent it from making a mess.
I run an two tanks (80 and 90) gallons on a sponge filter. The 80 is fairly busy with stocking. The biggest issues are noise with the air pump. This is why research for a quiet unit is important. Deep Blue also has a relatively cheap Air Pump that they make. The one on my 80 works well and is quieter than my Tetra Whisper. Whispers are noisy, get them at your own risk!
Internals, the few times I messed with them they were bulky and awkward to put into a tank and make it look right. I find an easier time squirreling the sponge filters out of the way and on a 15 gallon what you buy will be smaller.
Just to show you what one can do on a well balanced tank. I spent 30 bucks on the sponge + air pump. Don't mind the Rainbows, within the next week or two I'm going to solve their shoal size problem by either moving them to another tank, or getting more for that tank. There is 1 peacock eel, 14 loaches, 3 rainbows (6 soon I hope?). In the past this tank also had 17 Harlequin Rasbora.