Wow. What a neat coin. It comes from old German West Africa, called Tanganyika today. Germany acquired control of the area by treaties with coastal chiefs in 1884. After World War I, Tanganyika was entrusted to Great Britain and became an independent country in the British Commonwealth in 1961.
The gold 15 rupien coins are very popular with collectors. They contain 0.173 troy ounces of gold, but collector demand drives prices much higher than gold value.
worn: $800 US dollars approximate catalog value
average circulated: $1500
well preserved: $3000
fully uncirculated $4000
The trouble with these coins is that they are (1) rare, (2) valuable, and (3) really spiffy. This makes them a sure target for counterfeiters. Oodles of fake coins exist, and some are not obvious counterfeits. You must be careful when buying these coins; deal only with people you know and trust.
Some counterfeits are legal to own, and some collectors like to add legal reproductions to their collection. See, for instance, Ken Potter's page of World Gold Coin Reproductions [Press Here]. Ken has a gold plated silver replica on sale for $58.
If the coin has the word COPY on the front or the back, you can be sure it is not a genuine item.
The coin in our main picture comes from Emporium Hamburg where it sold for 2900 euros, about $3900 US dollars, during a 2014 auction.