Silvia is a bit of a learning curve, but I would say weeks rather than months.
I would suggest using a small milk jug for frothing to begin with (300ml).
Just under the half full mark. Make sure (whilst getting used to the machine) to wait for the steam light to go off before you begin the milk.
Purge any excess moisture from the steam wand before beginning.
Get the tip just on/under the level of the milk. Aim to get a whirlpool effect going and a little bit of air sucking in (many people call it the ch-ch-ch sound).
Once you get a little warmer, you can lower the wand (IE: Raise the jug) a little and just concentrate on the whrilpool.
It does take a little getting used to, but it certainly can be done on the Silvia.
If your shots are 15 seconds, then one or all of:
grind, dose, tamp
Try going a bit finer and see if there is a difference.
Try for more coffee in the basket.
Dont change too many things at once. Try just changing one thing at a time to see if you can isolate the most likely offender.