I have an idea... I tried dissolving tin, and yes it is slow. I also was trying to dissolve nickel, very slow also. I didn't want to use nitric acid, as I don't have any, and at the moment I don't want to deal with that.
After much thinking, I thought of increasing the temperature. I used a beaker on a hot plate set to around 1 or 2, but too much of either the water or HCL was boiling off fast. So I tried using a boiling flask with a rubber stopper with a small hole. Voila! I boiled the nickel button (a flattened sphere) for 3 days, (better than waiting potentially for several months!) till it was gone. Not only that, little of the liquid boiled away.
I bought a boiling flask that had an extra long neck, which I think also helps keep the liquid in.
Also, I tried boiling it at a setting of 2 which made the solution boil like mad, so I turned it down so there were few bubbles from the solution and mostly from the nickel.
Yes, 3 days is a long time, but it is MUCH better than the alternative.
So try that with tin. I am going to try it.