Gorgeous coins, these old Austrian gold ducats. Your 1915 example is one from a long line starting in 1852. They all contain 0.1106 troy ounces of gold.
On this page we address Austrian 1 ducat coins from 1867 to 1915. These 1 ducat coins measure about 20 mm in diameter; 4 ducat coins measure about 40 mm in diameter. Our page for Austrian 4 ducats appears at this link. Austrian 1 and 4 ducat gold coins are complicated subjects, as there are many subtle variations. Do not invest large sums in them unless you are sure you know what you are doing.
NOTE: If you are thinking of investing in gold coins, please read our article RIP FREE GOLD using the link at the upper left.
Coins dated 1915 -- These coins are restrikes, which means they bear a 1915 date but were actually struck later. They are bought and sold as bullion coins, i.e., for their gold content alone.
The value of the gold content is computed by finding the current spot price of gold at web sites like kitco.com. It changes every day, but at this moment one ounce of gold is worth $1088 US dollars. Your coin, is then worth 0.1106 x $1088 = $120 in gold content.
Coins dated before 1915 -- Two factors contribute to the value of pre-1915 coins: (1) gold content, and (2) rarity relative to demand from coin colletors.
The gold content is evaluated the same as the 1915 coins explained above. For the rarity factor, add (approximately) these values to the gold content:
circulated: add $10 US dollars
fully uncirculated: add $150
These additional values apply to all dates between 1867 and 1914.