1.5 Watt / 12volt = 0.13 Amps
0.13A / 3A-h = 0.043 or "C/23" charge ratio. Sounds fine to me. Skip the charge regulator.
-But-
For demonstration purposes, most people expect immediate, visible results. It's more likely that you will need to put a Load in the system, like a motor, a light, or whatnot, that DOES something when the sun shines. Once there's a load on the battery, you suddenly need a low-voltage disconnect. Otherwise the battery will spend 90% of its life run flat.
This turns your question about panel-vs-battery charging controller into a question on the other side: battery-vs-load control.
If you build a Ghurd kit, set up for load control, and mount it into a little clear perspex box, you will have something nifty to look at in the demo, and it will operate a little lamp or other "interesting" machine.